The family name, DATE, was derived from the county name "'Date" in Mutsu Province (present-day, the northern area of Nakadori, Fukushima Prefecture [specifically, the area covers Date City of Date County plus a part of Fukushima City]), but the county was originally called "Idate" or "Idachi" in ancient times and changed to "Idate" in the Medieval Period.
伊達の名は陸奥国伊達郡（現福島県・中通り北部…伊達市(福島県)、伊達郡、一部は福島市）に由来し、この地名は古代には「いだて」または「いだち」、中世以降は「いだて」と呼ばれた。