Census Records

Many of the census records are available free online at Archive.org. You can read and even download the massive files.

However, you may want to start looking with indexed 1880-1940 census records at FamilySearch:

Federal census for 1870, 1880, 1900, 1910, 1920, 1930, 1940

Census files restored from old Yuma AZGenWeb

Transcription of 1870 census index1
Transcription of 1870 census index2
Transcription of 1870 census file1
Transcription of 1870 census file2
Transcription of 1870 census file3
Transcription of 1870 census file4
Transcription of 1870 census townships