"United States Census, 1880," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MD2B-HQ7 : accessed 13 March 2016), Helen Luella Clark in household of Chas A Clark, Cedar Rapids, Linn, Iowa, United States; citing enumeration district ED 259, sheet 138A, NARA microfilm publication T9 (Washington D.C.: National Archives and Records Administration, n.d.), roll 0351; FHL microfilm 1,254,351.
"United States Census, 1900," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:M922-LMB : accessed 13 March 2016), Helen L Clark in household of Chas A Clark, Cedar Rapids city Ward 5, Linn, Iowa, United States; citing sheet 6B, family 89, NARA microfilm publication T623 (Washington, D.C.: National Archives and Records Administration, n.d.); FHL microfilm 1,240,444.