↑ Burgerlijke Stand Geboorten Winterswijk - Index extracten - Periode 1823-1832.
Hendrik Jan, z.v. Jan Albert Koijers, 39 jaar, landbouwer, wonende op Leefferdink in buurschap Ratum, en Gesiena Keveskamp; geboren 9-4-1826 (akte nr.66)
"United States Census, 1850," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MF8L-53L : accessed 17 January 2015), Hendrik Tan Kooyers, Holland, Ottawa, Michigan, United States; citing family 21, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).