Lapinjärvi (; ) is a municipality of Finland. It is located in the Uusimaa region. The municipality has a population of and covers an area of of which is water. The population density is .
Neighbouring municipalities are Iitti, Kouvola, Loviisa, Myrskylä and Orimattila.
The municipality is bilingual, with majority being Finnish and minority Swedish speakers.
Lapinjärvi lake is located in the Lapinjärvi.
Lapinjärvi is a rather small lake in the middle of the Lapinjärvi municipality in Uusimaa region, Finland. There are 27 small lakes in Finland with the same name.
Lapinjärvi may refer to:
- Lapinjärvi (municipality), a municipality in Finland.
- Lapinjärvi (lake), a lake in the above municipality.