"United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M9SK-WMD : accessed 9 August 2017), Thora Heller in household of Thomas Heller, Election District 1 Minneapolis city Ward 10, Hennepin, Minnesota, United States; citing enumeration district (ED) 105, sheet 19A, family 332, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, 1972.); FHL microfilm 1,240,769.
"United States Census, 1920," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MWY6-1H9 : accessed 9 August 2017), Thora Heller in household of Thomas S Heller, Minneapolis Ward 3, Hennepin, Minnesota, United States; citing ED 48, sheet 10A, line 16, family 226, NARA microfilm publication T625 (Washington D.C.: National Archives and Records Administration, 1992), roll 832; FHL microfilm 1,820,832.
"United States Census, 1930," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:X3ZN-9ZN : accessed 9 August 2017), Thora Calkin in household of Charles E Hermann, Minneapolis (Districts 318-328), Hennepin, Minnesota, United States; citing enumeration district (ED) ED 323, sheet 20A, line 43, family 198, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 1092; FHL microfilm 2,340,827.
"United States Census, 1940," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:KSV5-KN4 : accessed 9 August 2017), Thora Calkin in household of Thomas S Heller, Ward 3, Minneapolis, Minneapolis City, Hennepin, Minnesota, United States; citing enumeration district (ED) 89-43, sheet 3A, line 32, family 58, Sixteenth Census of the United States, 1940, NARA digital publication T627. Records of the Bureau of the Census, 1790 - 2007, RG 29. Washington, D.C.: National Archives and Records Administration, 2012, roll 1977.