"United States Census, 1910," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MLRN-334 : 29 October 2015), Roelofje Kolkema in household of Lewis Kolkema, Muskegon Ward 2, Muskegon, Michigan, United States; citing enumeration district (ED) ED 81, sheet 11A, NARA microfilm publication T624 (Washington, D.C.: National Archives and Records Administration, n.d.); FHL microfilm 1,374,680.