Lohjanjärvi (Swedish: Lojo sjö) is a lake in Uusimaa region in southern Finland. The biggest part of the lake is located in the town of Lohja and smaller parts in the municipality of Karjalohja and in the town of Raseborg (Finnish: Raasepori). The lake drains into the Gulf of Finland through the Mustionjoki River (aka Karjaanjoki, Swedish: Svartån).