"Iowa, County Marriages, 1838-1934," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:XJJQ-XMD : 27 September 2017), Olof Nelson and Karoline Danelson, 19 Jul 1899, Fairfield Twp, Buena Vista, Iowa, United States; citing reference it 2 mr 3 p 145, county courthouses, Iowa; FHL microfilm 1,428,712.
"Iowa, County Births, 1880-1935," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:XV6B-Y73 : 1 April 2020), Olof Nilson in entry for Carl David Nilson, 28 Jun 1900; citing Iowa, United States; county district courts, Iowa; FHL microfilm 1,428,655.
"United States Census, 1910," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:ML14-CLV : accessed 17 February 2023), Olof Nelson, Fairfield, Buena Vista, Iowa, United States; citing enumeration district (ED) ED 3, sheet 7A, family 124, NARA microfilm publication T624 (Washington D.C.: National Archives and Records Administration, 1982), roll 394; FHL microfilm 1,374,407.
"Iowa State Census, 1925," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:QKQW-2ZJS : 8 August 2022), Olaf Nelson, Elk Township, Buena Vista, Iowa, United States; citing Elk Township, Buena Vista, Iowa, United States, Iowa State Historical Department, Des Moines; FHL microfilm .
"United States Census, 1930," database with images, FamilySearch (https://www.familysearch.org/ark:/61903/1:1:XMNF-S5Y : accessed 17 February 2023), Olof Nelson, Fairfield, Buena Vista, Iowa, United States; citing enumeration district (ED) ED 7, sheet 3B, line 74, family 80, NARA microfilm publication T626 (Washington D.C.: National Archives and Records Administration, 2002), roll 645; FHL microfilm 2,340,380.
Evangelical Lutheran Church in America, Swedish American Church Records, 1800-1947, Our Saviors Lutheran Church Albert City Iowa Members List, Archives of the Evangelical Lutheran Church in America; Elk Grove Village, IL, USA; Swedish American Baptisms, Marriages, Deaths, and Burials; Parish: Our Saviors Lutheran Church; ELCA Film Number: A198(1+2); SSIRC Film Number: A198, https://www.ancestry.com/sharing/1861568?mark=6bc853d3b9336785ee3cd111bed3b3f928ee6446fe73e27667de2a4f89f2dbaf