It is 37.3 kilometers (23.2 mi) in length and has a drainage area of 222 square kilometers (86 sq mi).

The river basin of the Ichinomiya was a social, cultural, and economic center of Kazusa Province in pre-modern Japan.

Although very shallow, the river was used to transport sardines from Kujukuri Beach to Tokyo Bay until the beginning of the Meiji period.

The source of the Ichinomiya River is in the Fukusawa District of Chōnan, and crosses the southern part of the Kujukuri Plain through Ōtaki, Nagara, Mobara, and Mutsuzawa, and the town of Ichinomiya.

It pours into the Pacific Ocean in the Ichimatsu District of the village of Chōsei.