Situated 70 kilometres suth-west of Rustenburg. Koster derives its name from Bastiaan Hendricus Koster, a native of Rotterdam, born in 1860. At the turn of the century he was a local farmer living on the farm Kleinfontein, and he consequently named the town after himself. It assumed some importance after the opening up of the railway line between the Witwatersrand and Mafikeng, when a siding was established there.
A map showing the Rustenburg District.
It became a village in 1913 and was given municipal us in 1930. The Dutch Reformed Church started a mission in Koster in the 1920s. On 11 November 1970, one of the last diamond rushes in South Africa took place in Koster when 167 diggers rushed to stake their claims. Slate was found nearby and Koster is now predominantly a slate mining and agricultural centre.