Iwai Family (石井家)
The Iwai family, which claimed to be descended from the Kanmu-Heishi (Taira clan) TAIRA no Takamune-o line, beloged to the Tosho-ke (the hereditary lineage of Court nobles occupying relatively high ranks). 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.
There was a rather complex background to the establishment of the Iwai family as follows; though the first Yukitoyo was a son of Tokitsune HIRAMATSU of the Shonii Gon Chunagon (Senior Second Rank, Provisional Vice-Councilor of State) (1627 -1704), Emperor Gomizunoo and Tofukumonin allowed Yukitoyo to establish a new family in appreciation of his service in his adoptive family, Iwai no tsubone. The family was named after Gyoshi's common name (Iwai no tsubone) in the court.
The hereditary stipend was 130 koku in the Edo period. The family had been given the title of viscount since the Meiji period.