It is located in the province of Southern Finland and is part of the Uusimaaregion. Before merging into Lohja, the municipality had a population of 1,474 (31 December 2012)[2] and covered an area of 163.40 square kilometres (63.09 sq mi) of which 42.11 km2 (16.26 sq mi) was water.[1] The population density was 12.153/km2 (31.475/sq mi).
With Nummi-Pusula, Karjalohja was consolidated with the town of Lohja on 1 January 2013.[3]