It is considered that his common name, 'Sakai' was derived from the fact that the foothold of the Chiba clan was located in the watershed of Sakai-gawa River, which is running through the outskirt of their base territory, Chiba no sho (the private estate of the Chiba clan); later he also reigned Habu no sho in Shimousa Province and Tamasaki no sho in Kazusa Province, and established his foothold at Oyanagi no tate (currently Mutsuzawa-cho, Chiba Prefecture) in Tamasaki no sho; he further expanded his territory to the opposite shore of Sakai-gawa River from Chiba no sho, Ichihara District in Kazusa Province.
通称である「境」は千葉氏の本拠である千葉荘の外れにあった境川（現在の村田川）流域に拠点があったからとされ、後に下総国垣生荘及び上総国玉崎荘などを支配して玉崎荘の大柳館（現在の千葉県睦沢町）を拠点とし、更に千葉荘とは境川対岸の上総国市原郡にも進出することになる。