| Ichinomiya River | |
| Source1 Location: | Fukusawa District, Chōnan, Chiba Prefecture |
| Mouth Location: | Pacific Ocean |
| Subdivision Type1: | Country |
| Subdivision Name1: | Japan |
| Length: | 37.3km (23.2miles) |
| Mouth Elevation: | 0m (00feet) |
| Basin Size: | 222km2 |
The is a river in Chiba Prefecture, Japan. It is 37.3km (23.2miles) in length and has a drainage area of 222km2. Under the Rivers Act of 1906 the Ichinomiya is designated as a Class 2 River. 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.