FamilySearch (https://familysearch.org/ark:/61903/1:1:X1QW-1Y3 : 10 February 2018), Frederik Koolhof, 21 Jul 1889; citing Scheemda, Groningen, Netherlands; FHL microfilm 446,661. - Frederik Koolhof, "Netherlands Births and Baptisms, 1564-1910" » Les sources » Arbre généalogique familie Steenhuis » Généalogie Online"> FamilySearch (https://familysearch.org/ark:/61903/1:1:X1QW-1Y3 : 10 February 2018), Frederik Koolhof, 21 Jul 1889; citing Scheemda, Groningen, Netherlands; FHL microfilm 446,661. - Frederik Koolhof, "Netherlands Births and Baptisms, 1564-1910" » Les sources » Arbre généalogique familie Steenhuis » Généalogie Online">
"Netherlands Births and Baptisms, 1564-1910," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:X1QW-1Y3 : 10 February 2018), Frederik Koolhof, 21 Jul 1889; citing Scheemda, Groningen, Netherlands; FHL microfilm 446,661. - Frederik Koolhof, "Netherlands Births and Baptisms, 1564-1910"