The Ohinemuri County Council first met on 17 November 1885. It was formed from a portion of Thames County. A 1919 petition resulted in loss of the western part of the area to a new Hauraki Plains County in 1920.
The population was 1,516 in 1891, 3,056 in 1945 and 5,579 in 1986.
In 1923 Ohinemuri County covered 253 sq mi (660 km) and had a population of 2,678, with 66 mi (106 km) of gravel roads, 55 mi (89 km) of mud roads and 50 mi (80 km) of tracks.
The 1911 Italianate county offices at 41 Belmont Road, Paeroa, were used by the county until 1986. They are now used by Hauraki Māori Trust Board and protected by an A Category listing in Hauraki District Plan.
