- 1928-10-25: The completed Hakubi Line is opened.
- 1929-04-14: Sakubisai Line (which became the Kishin Line) section opened.
- 1930-02-10: The fork from Bitchū Kōjiro Station is opened with regular service to Niimi Station.
- 1987-04-01: With the privatization of the Japanese National Railways, Niimi Station becomes a JR West station.
The station uses the two-sided island style of platform, allowing for up to four lines to use the station at once (see the platform photos to the right). No freight trains pass through this station as it is designed to handle only passenger trains. Restrooms are located on the side of the station building. The automatic announcement system does not use the standard "The X train is arriving at platform Y." Instead, the announcement tells which line is arriving or departing. Tickets are handled using JR West's HeartStore.
The platform island is connected to the station building via an underground tunnel, and the platform features a large enclosed waiting room in addition to the outside waiting area on the platform. The various train lines served by Niimi Station are handled as follows:
Many businesses and services are located near Niimi Station. Following is a list of some of them:
- A-Coop (an agricultural cooperative)
- Bitchū Railway Office (JR West)
- Café de Shirube (including a wireless access point)
- The local Japan Agricultural Cooperatives offices
- The Niimi Post Office
- Niimi Interchange of the Chūgoku Expressway
- Route 180
- Route 182
- Okayama/Tottori Prefectural Route 8, Niimi Nichinan Route
- Okayama Prefectural Route 32, Niimi Katsuyama Route
- Okayama Prefectural Route 199, Niimi Teishajō Route
All lines are JR West lines.
- Hakubi Line
- Ishiga Station — Niimi Station — Nunohara Station — Bitchū Kōjiro Station
- Kishin Line
- Express: Osakabe Station — Tajibe Station — Iwayama Station — Niimi Station
- Local: Iwayama Station — Niimi Station
- Geibi Line
- Express (one early morning train only): Niimi Station — Yagami Station
- Local: Niimi Station — Nunohara Station
- (in Japanese) JR West