John Ernest Mitchell Heffelbower (or Heffelbower) was the younger of two children born to David F. Heffelbower (1836–1897) and Susannah Virginia "Susie" Mitchell (1837–1894). John's older sister was Dora Elizabeth Heffelbower (1861–1894).

David was born and grew up in Lucas County, Ohio, and married Susie in 1859 in Albany, Whiteside County, Illinois. The 1860 Census lists him as a carpenter in nearby Newton, Illinois. By 1880, he was a carpenter living in Denison, Texas. In 1891, he had a shop on the west side of Mirick Avenue between Monterey and Heron Streets. Then, by 1896, he had a shop at 600 West Monterey selling "lumber, paints, oil, etc." He lived nearby at 608, while his son John was living at 612. David died the next year. Both he and Susie were buried in Fairview Cemetery in Denison.

At the end of 1880, Dora had married George Alfred Lake (1860–1944) in Denison. He was a Canadian who had immigrated to the U.S. after 1861 with his parents and siblings. In the 1870 Census, the family was in New Jersey but had moved to Denison in 1878. In 1880, George and his father, Samuel Bell Lake (1822–1887), were carriage makers on Denison's Chestnut Street. Samuel and wife Rebecca (1830–1890) were both buried in Fairview Cemetery. George was still a "carriage painter" in 1900, but as automobiles became more popular, the carriage trade dried up. By 1903, George's occupation was "insurance solicitor." That year, George, Dora, and daughter Georgia V. Lake Clark (1883–1964) moved to Dallas. The 1930 Dallas City Directory listed him as representative of American Transfer & Storage, as well as president of the Texas State Humane Society.

Meanwhile, John E.M. Heffelbower, the carpenter's son and Dora's brother, had become a dentist.  At age 18, in 1891, he was working as assistant to Dr. W.H. Mills, dentist above 217 West Main Street.  Then he left to study at the University of Maryland's Department of dentistry in Baltimore, graduating in 1894.  While there, he married Lula Ethel Wilson.

 
Source: "Busy Dentist," ed. Thomas H. Hinman, vol. 1, page 158 (Mutual Printing Company). 

They moved back to Denison, and he and Dr. Mills teamed up as Mills & Heffelbower.  In 1895, the practice was located on the second floor of the elegant National Commercial College Building.  In 1896, the Heffelbowers had a daughter, Marie.  For a few years they lived at his old place, 612 Monterey, and then at 606 West Monterey.  

By 1901, Dr. Mills and Dr. Heffelbower had gone separate ways.  John was on his own, with an office in the Ford Building (later the
Citizens National Bank), at 231 West Main.  

"Office of J. E. M. Heffelbower, Dentist, Ford Building."
231 West Main Street
Robinson, Frank M., comp. Industrial Denison. [N.p.]: Means-Moore Co., [ca. 1909]. Page 49.

In 1910, John, Ethel, and Marie were living at 423 West Gandy, in the home of John Shuel.  In 1913, they were living at 531 West Gandy.  By 1917, John's office was on the fourth floor of the Security Building, at 331 West Main, where it remained for may years; and the family was living at 630 West Gandy.  Marie married Edwin Miller of Denton in 1919.

The Denison Herald
Saturday, July 12, 1919
pg.8

HONORING MISS HEFFLEBOWER
In compliment to Miss Marie Hefflebower, who is soon to become the bride of Edwin Miller of Denton, Mrs. Ray Clymer entertained with a miscellaneous shower Thursday morning at her home, 931 W. Morton street.
The living room and library were arranged with tables for the playing of auction bridge and here a scientific series of cards claimed the attention of the guests.  There were 8 tables of players.  At the conclusion of a stipulated number of progressions, Mrs. Robert Foster of Muskogee was found to be  holder of top score and received the prize, a dainty article of silk lingerie, which she presented to the honor guest.  The honoree's favor which went to Miss Hefflebower was a set of cut glass almond dishes.
After the games a charming little figure in the person of little Miss Mavis Clymer appeared attired in overalls and drawing a wagon filled with pretty gifts.  The idea was a very clever one as Miss Heffelbower after her marriage will be a bewitching farmeritte, her husband being a ranchman.  After the lovely gifts had been examined and enthused over, Mrs. Clymer's guests were served with brick ice cream and cake. (Editor's note: "Little Miss Mavis Clymer" was the mother of Dr. Mavis Anne Bryant and at the time, according to her son, was a year and nine months old.)

In 1929, John and Lula lived at 1325 West Woodard Street.

John's sister, Dora Heffelbower Lake, died in 1935.  In 1933, looking forward to the Texas Centennial, a special pecan tree honoring Sam Houston had been planted on the grounds of the 1914 Denison High School on the 700 block of West Main Street.  Now a bronze plaque was placed at the bottom of the tree by Dora's grieving husband, Lt. Col. George A. Lake.  As "president of the Texas Historic Nut Planting Association," George chose this way to honor General Houston, the Texas Centennial, Dora and his own Denison heritage.  

By 1940, an aging Dr. John Heffelbower had moved to an office upstairs in the State National Bank Building.  He and Ethel now lived upstairs at 513 West Gandy; this was the home of Harry Tone, Jr.  John passed away on October 6, 1947.  Ethel died six years later.  Both are buried in Fairview Cemetery in Denison.