Linn County, situated in the eastern tier, next to the Missouri state line, and in the third tier south of the Kansas river, was one of the original 33 counties created by the first territorial legislature, with the following boundaries: "Beginning at the southeast corner of Lykins (now Miami) county; thence south 24 miles; thence west 24 miles; thence north 24 miles; thence east 24 miles to the place of beginning."

It was named Linn in honor of Lewis F. Linn, a United States senator from Missouri. In 1868 the boundaries were redefined as follows: "Commencing at the southeast corner of Miami county; thence south along the west boundary of the State of Missouri to the corner on said line to fractional sections 13 and 24, township 23 south, of range 25 east; thence west along the section lines to the corner of sections 14, 15, 22 and 23, township 23 south of range 21 east; thence north along the section lines between the second and third tiers of sections to the southwest corner of Miami county; thence east along the south boundary of said Miami county to the place of beginning."

By this act a strip, varying in width from a half mile at the northwest corner of the county to nearly a mile and a half at the southwest corner, was added to the west side of the county and the area increased to 637 square miles. It is bounded on the north by Miami county, on the east by the State of Missouri, on the south by Bourbon county, and on the west by Anderson county, and is divided into eleven townships: Blue Mound, Centerville, Liberty, Lincoln, Mound City, Paris, Potosi, Scott, Sheridan, Stanton and Valley.

The general surface of the county is undulating, rather broken in the eastern part, and about one-tenth is too rough for cultivation. One-fifth is rich bottom land, very fertile and productive. The upland or rolling prairie is generally from 50 to 80 feet above the valleys, the highest elevation being Silver Hill, near the Marias des Cygnes, which rises to a height of 300 feet above the river. The timber belts along the streams are usually nearly as wide as the valleys, the principal varieties being black walnut, oak, sycamore, hickory, cottonwood, ash, box-elder and elm. The most important water course is the Marias des Cygnes, which crosses the northern boundary a little east of the middle and flows in a southeasterly direction, crossing the eastern boundary a little north of the center.

The first white man to visit the country now embraced within the boundaries of Linn county was probably Dutisne (q. v.) in his expedition of 1719. The first white men to remain for any time in what is now Linn county were Girard and Chouteau, who in 1834 established a trading post on the north branch of the Marias des Cygnes in what is now Potosi township. In 1839 the Catholics established a mission among the Pottawatomie Indians near the site of the present town of Centerville. It was removed to St. Mary's in 1847. It is believed that the French came up from Louisiana and encouraged the Indians to mine lead on Mine creek, from which it derived its name, but the extent of this industry is conjectural and it was early abandoned by the French as unprofitable. It was the French who named the Marais des Cygnes from the many swans on the swamps along the river and so called it the "Marsh of swans."

As soon as it became apparent that the territory west of Missouri would be thrown open to white settlement many squatters located claims along the wooded streams of Linn county, mostly by pro-slavery men from Missouri, who cared little for progress and desired to preserve the institutions to which they were accustomed. Some of these early settlers were James Osborne and Adam Pore, who in Jan., 1854, took claims at the head of Sugar creek, near the present town of Mound City. D. W. Cannon, William Murray, John Brown, James Montgomery, James Osborne and William Park all came that year to what is now Linn county. Trouble soon arose between the free-state and pro-slavery parties, as it was impossible for men of such different political beliefs to live together in harmony. The first convention, and one of the first causes of trouble, was held at Sugar Mound Feb. 20, 1855. It was called for the purpose of nominating a candidate for the territorial legislature. It was called by James Fox, a pro-slavery leader, and few of the free-state settlers were notified of the convention. James Montgomery, who was secretary of the convention, succeeded in having it adjoined in order that more settlers might be present. A second convention was therefore held, but the free-state men were defeated at both the convention and at the election held on March 30.

Linn county sent three delegates to the Lecompton constitutional convention, J. H. Barlow, S. H. Hayze and George Overstreet. The free-state men generally failed to vote at the election for these candidates. At the election for officers under the Lecompton constitution, held at Sugar Mound, the free-state men of the county voted, not knowing that the convention which had assembled at Lawrence on Dec. 2, had adopted resolutions repudiating the constitution. James Montgomery learned of these resolutions on the day of election and going to the polls told the free-state voters that they had been misinformed as to the decision of the true convention, seized the ballot box, broke it to pieces and destroyed the ballots.

Mound City was started in the spring of 1855 by the opening of a store there by a man named Miller and it soon became a well known pro-slavery headquarters, although the town was not organized until 1857. Trading Post was one of the early settlements, both free-state and pro-slavery men locating in the vicinity, but in time it became a stronghold of the latter party. Paris, situated about 6 miles south of Mound City, was owned by pro-slavery men and in the early days became a rallying point from which to make raids upon the free-state settlers. Up to the middle of the summer of 1856 there was comparatively little trouble between the two political factions in the county. Difficulties arose over claims, and much of the trouble for years was laid at the door of G. W. Clark, who it was claimed burned a number of free-state settlers out of their homes. It is true that he did burn several cabins, but never the number reported.

In the summer of 1856 the Missourians were gathering armed forces along the border under the leadership of Atchison, Reid and Clark. Capt. John E. Davis was camped with a force of 150 men on Middle creek in the northwest corner of the county. On Aug. 24, Capts. Anderson, Shore and Cline, with a command of about 125 men, camped in the same locality. In the morning scouts of the free-state party brought in word that about 50 of Davis' men were absent from camp and an attack was immediately planned. When the free-state men came within range the Missourians opened fire, which was immediately returned. The firing lasted about ten minutes before the Southerners retired. In the action Lieutenant Cline was wounded and subsequently died. This affair is known as the battle of Middle Creek. In the fall the Missourians raided Linn county. They first went to Paris, where they were joined by some of the settlers, then moved on to Sugar Mound, where they burned some houses, robbed Ebenezer Barnes' house, the store and the postoffice. Many depredations were committed and the free-state settlers warned to leave the county. This and like raids influenced James Montgomery to gather a company of courargeous[sic] free-state men, which started out on raids of retaliation into Missouri. This brave band was so daring, and meted out vengeance[sic] in such a summary manner, that Montgomery became known as the Jayhawk leader and was greatly feared by men of the opposite party.

The leader of the pro-slavery party was Charles Hamelton, and Trading Post was his acknowledged headquarters. When the Missourians warned the free-state settlers to leave the county Montgomery raided Trading Post with the intention of breaking up the headquarters of Hamelton's gang. They did not kill or harm anyone, but poured out all the whisky found in the store and warned the pro-slavery settlers to leave, saying that there was not room enough for both in the county. As a result of this raid Hamelton led the party which committed the Marais des Cygnes massacre (q. v.). After this atrocious affair the persons who took part in it disappeared. Another free-state leader who arose at this time was C. R. Jennison, who became known as one of the greatest leaders during the border warfare.

In the Civil war Linn county was represented in the Second Kansas infantry, the Sixth cavalry, the Tenth infantry, the Seventh cavalry, the Twelfth infantry and Fifteenth cavalry; many men also enlisted in the regular army of the United States. During the war raids from Missouri were common, and raids from Linn county into Missouri were nearly as frequent. In Oct., 1861, a party of Missourians under Sheriff Clem of Bates county raided Linn county, killed several men and robbed a number of houses. In December a party of about 125 Missourians again raided Linn county, robbed and pillaged houses, killed one Union man, and others barely escaped with their lives by hiding. A Union force retaliated by marching into Missouri, but being met by a stronger force retired into Kansas. After this raid Camp Defiance was established on Mine creek in Linn county, near the Missouri line, and Col. Montgomery with the Third regiment was stationed there until the spring of 1862. The most important and exciting event of the Civil war which occurred in Linn county was the Price raid, in which battles occurred at Mound City on Oct. 25; at Round Mound, about 6 miles from the river; and at Mine creek, 4 miles south of Round Mound. (See Mine Creek.)

The first store in Linn county was at the Trading Post for trade with the Indians, though the first whites in the county also bought goods there. The first postoffice was opened at Mound City, at the store of a Mr. Miller, who was appointed postmaster in the spring of 1855. The first school in the county was held during the winter of 1858-59 in the town hall at Blue Mound, and the first marriage solemnized in the county was that of J. S. Atkins and Maria Mannington in 1858. The Methodist Episcopal church was the pioneer religious organization in the county. They were followed by the Baptists and United Brethren, both of whom erected churches in Mound City in the early '60s.

Linn county was organized in 1855. The first board of county commissioners—called a court—consisted of R. E. Elliott, president, L. M. Love and Brisco Davis. They appointed James F. Fox, treasurer; Joseph D. Wilmot, clerk; James Driskill, assessor; William Rogers, surveyor; Joseph E. Brown, sheriff; and Elisha Tucker, coroner. On the same day these officers were appointed the court divided the county into three municipal townships: Scott, Johnson and Richland. Subsequently changes were made in both the divisions and names until the present eleven townships were created.

By the act creating the county provision was made for the election of commissioners on the second Monday of Oct., 1855, and that the "commissioners so appointed for the county of Linn shall locate the county seat of said county within 3 miles of the geographical center." There is no record available to show that this board was ever elected, but on Jan. 18, 1856, the county commissioners appointed a commission to locate the county seat. On March 18 James P. Fox and a man named Osborne, the only commissioners who acted, made a report that they had decided on the northwest quarter of section 8, township 21, range 24. The town (named Paris) was laid out by William Rogers, the county surveyor. The board of county commissioners held their first meeting there on Aug. 7 in the house purchased from J. P. Fox, who owned the land. This location was not satisfactory to any of the residents and an election to relocate the county seat was held on Nov. 8, 1859, when Mound City was chosen, the first meeting of the county board being held there Dec. 15. On May 30, 1865, the county seat was changed to Linnville, a town just south of the site of Paris and a few miles north of Mound City. On Feb. 20, 1866, still another election was held to relocate the county seat, at which time Mound City was again chosen. An election was then held May 29 on the same question, the result being that Mound City retained the county seat. On Feb. 14, 1871, the seat of justice was changed to La Cygne by the vote of the people; on March 27, 1873, the seat of justice was changed to Farmers City, but as the location was a mere brush patch the county officers refused to go there, and La Cygne remained the county seat de facto until April 14, 1874, when an election was held at which Pleasanton received the majority of votes. The question of the permanent location was still undecided and in 1875 a decisive and last election was held, when Mound City was chosen as the seat of justice of Linn for the third time, where it has since remained.

The first railroad in Linn county was the Kansas & Neosho Valley. A proposition was made for the county to issue $150,000 worth of bonds with which to buy stock of the railroad, but as the county officials and the railroad officials could not agree this was never done. The road was built, however, but was located in the eastern part of the county. At the present time there are over 90 miles of main track railroad in the county. The St. Louis & San Francisco crosses from north to south along the eastern boundary through Pleasanton with a branch into Missouri. The Missouri Pacific crosses the southern part of the county east and west, branching at Blue Mound in the southwest, one branch running west into Anderson county and the other south in Bourbon county. The Missouri, Kansas & Texas enters in the northwest and crosses south into Anderson county. These lines provide excellent transportation and shipping facilities for all portions of the county except the center.

The chief agricultural products of Linn county are corn, flax, winter wheat, oats, Kafir corn and hay. Live stock is a profitable industry. There are more than 125,000 bearing fruit trees in the county, which bring in a considerable revenue. Common and magnesium limestone are plentiful and large quarries are operated near Pleasanton; salt springs exist in the southern portion; coal of a good quality underlies a considerable part of the county and has for many years been mined in commercial quantities for exportation; cement rock abounds and clay is plentiful in the southeast; oil and natural gas have been found near Pleasanton, and the latter is used for heating and lighting. Pleasanton is the largest town in the county. Mound City, the seat of justice, is 81 miles south of Kansas City and is a shipping point for a rich district. La Cygne is also an important town. The population of Linn county in 1910 was 14,735, and the value of her agricultural products, including live stock, was $2,219,376.