1844 Birth:821,2276 Birth year of 1844 is estimated based on age of 6 in 1850 census enumeration and age of 36 in 1880 census enumeration. Birth place of Porter County, Indiana is assumed as his parents were enumerated there in both the 1840 and 1850 census enumerations, the latter household led by the widow Margaret McCoy.

1850 U.S. Census:821 Oliver P. enumerated in the household of his widowed mother Margaret McCoy in Porter Township, Porter County, Indiana as a male, age 6, born in Indiana.

1870 U.S. Census:2317 Oliver enumerated in the household of his brother Weaden McCoy in Colusa Township, Colusa County, California as a male, age 26, white, farm laborer, $600 personal property value, born in Indiana, male over 21. Weaden McCoy's2317 household also included mother Margaret McCoy and was enumerated as the last of a group of three households beginning with brother John McCoy2318 and family, with brother Francis McCoy2316 and family enumerated as the second household.

1880 U.S. Census:2306
Tehama County, California (Township 26 N.R. 6 West)
Enumerated 11 June 1880
Oliver P. McCoy •• white, male, 36, married, farmer, born in Indiana, father born in Kentucky, mother born in Kentucky
Addie M. •• white, female, 22, wife, married, keeping house, born in Indiana, father born in Indiana, mother born in Indiana
Viola R. •• white, female, 4, daughter, single, born in California, father born in Indiana, mother born in Indiana
Della R. •• white, female, 2, daughter, single, born in California, father born in Indiana, mother born in Indiana

1885 Tehama County Directory:2020 O. P. McCoy, farmer, Red Bluff, California.