Kuniuji IMAGAWA, the second son of Osauji KIRA who founded the Kira family as the first illegitimate child of Yoshiuji ASHIKAGA (the third head of ASHIKAGA family), was given Imagawa no sho (the current Imagawacho, Nishio City, Aichi Prefecture), Aomi County, Mikawa Province) and called himself Shiro IMAGAWA (or it is said that Kuniuji was a nephew of Osauji and became an adopted son).
足利義氏(足利家3代目当主)の庶長子として吉良家を興した吉良長氏の2男である今川国氏が、吉良氏の所領から三河国碧海郡今川荘（いまがわのしょう、現在の愛知県西尾市今川町周辺）を分与され、今川四郎を称したのに始まる（あるいは国氏は長氏の甥で、養子になったとも言う）。