Later, Shigenari took as his wife a younger sister of Masako HOJO, who was Yoritomo's lawful wife; he was approved to be the landowner of the vast Inage no sho situated in the Tama Hills, constructed Masugata Castle (present-day Ikuta Ryokuchi Park) in Masugata-yama Mountain and called himself by the name of INAGE.
その後頼朝の正室北条政子の妹を妻に迎え、多摩丘陵にあった広大な稲毛荘を安堵され、枡形山に枡形城（現生田緑地）を築城、稲毛氏と称した。