For generations the family managed the Kurita estate of Oishi manor (currently Oishi-Higashi cho and Oishi-Naka cho districts in Otsu City, Shiga Prefecture) under the Omi-no-kuni shugo (Military Commissioner of Omi-no-kuni) of the Sasaki clan, and thus the family name became OISHI.
代々近江国守護佐々木氏のもとで栗太郡大石庄（滋賀県大津市大石東町・大石中町）の下司職をつとめていたため、大石を姓にするようになった。