The founder of the family was Yukitoyo IWAI (Junii Gon Chunagon, or Junior Second Rank, Provisional Vice-Councilor of State) (1653 - 1713), who was an adopted son of Gyoshi (Iwai no tsubone) who was a daughter of Tokiyoshi NISHINOTOIN (Junii Sangi, or Junior Second Rank, Councilor) (1552 - 1640) and served Tofukumonin (Kazuko TOKUGAWA) as a court lady.
東福門院（徳川和子）付きの女官で西洞院時慶（従二位・参議）（1552年〜1640年）の娘行子（石井局）の養子となった石井行豊（従二位・権中納言）（1653年〜1713年）を祖とする。