Previously, most biographies surmised that he was born in East Flanders, either in the town after which he was named (present-day Okegem, from which his ancestors must have come) or in the neighboring town of Dendermonde (French: Termonde), where the surname Ockeghem occurred in the 14th and 15th century.
Varasemates biograafiates oli enamasti oletatud, et ta sündis Ida-Flandrias, kas linnas, mille järgi ta oli nime saanud (tänapäeva Okegem, kust ta esivanemad olid ilmselt pärit), või selle naaberlinnas Dendermondes, kus 14. ja 15. sajandil leidus perekonnanime Ockeghem.