His grandfather Motoyoshi SHIMOGAWA served as a vassal to Kiyomasa KATO, and Keichu's father Mototsada was initially a feudal retainer of the Amagasaki clan but later became a ronin (samurai who left his master and lost his horoku [salary]).
祖父下川元宜は加藤清正の家臣であったが、父元全は尼崎藩士から牢人となる。