Tadatsune's descendants remained as powerful samurai in Boso Peninsula and formed the Kazusa clan and the Chiba clan which became gokenin (an immediate vasal of the shogunate) in the Kamakura bakufu (Japanese feudal government headed by a shogun) afterwards.
忠常の子孫は房総半島の有力武士として残り、後に鎌倉幕府の御家人となる上総氏、千葉氏が出た。