"United States Census, 1850," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:M44N-323: 21 December 2020), Martha Morris in household of Uriah Morris, Independence Township, Beaver, Pennsylvania, United States; NARA microfilm publication (Washington, D.C.: National Archives and Records Administration, n.d.).
"Iowa, County Marriages, 1838-1934," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:XJNW-W5L: 3 November 2017), William R. Mckinley and Martha M. Morris, 18 Feb 1858, Lucas, Iowa, United States; county courthouses, Iowa; FHL microfilm 1,009,237.
"United States Census, 1880," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:MD21-PXL: 14 January 2022), Martha McKinley in household of Wm. R. McKinley, Washington Township, Lucas, Iowa, United States; citing enumeration district 103, sheet 514C, NARA microfilm publication T9 (Washington, D.C.: National Archives and Records Administration, n.d.), FHL microfilm.
"Iowa State Census, 1885," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:HD9V-SPZ: 2 March 2021), Martha Mckinley in household of William R Mckinley, Washington, Lucas, Iowa; citing p. 24, 1885, State Historical Society, Des Moines; FHL microfilm 1,021,493.