Pornainen (Finnish: [ˈpornɑi̯nen]; Swedish: Borgnäs) is a small municipality of Finland. It is located in the province of Southern Finland and is part of the Uusimaa region. The neighboring municipalities are Askola in the east, Mäntsälä in the north, Porvoo in the southeast and Sipoo in the southwest. It is located 18 kilometres (11 mi) east of the town of Järvenpää.
The municipality has a population of 4,964 (30 June 2025) and covers an area of 150.09 square kilometres (57.95 sq mi) of which 3.59 km (1.39 sq mi) is water. The administrative centre of municipality is Kirveskoski (about 2,000 residents), also known as Pornainen's church village, and second largest village is Halkia (about 500 residents). The population density is 33.88 inhabitants per square kilometre (87.7/sq mi).