[2] The exact location of the capital of Kazusa is not precisely known, but is believed to have been somewhere within the borders of the modern city of Ichihara, Chiba.

The kokubun-ji was first excavated in 1949, and is on a plateau 30 metres (98 ft) above the Yōrō River in close proximity to Tokyo Bay.

However, by the Sengoku period, the Satomi clan had gained control over much of Awa, Kazusa and Shimōsa provinces.

The Satomi provided only lukewarm support to Toyotomi Hideyoshi during the Battle of Odawara against the Later Hōjō clan and were subsequently deprived of their holdings in Kazusa and Shimōsa.

During the Edo period, several small domains were created within the borders of Kazusa, most of which continued to be retained as tenryō territory owned directly by the shōgun and administered by various hatamoto.