is a municipality in Telemark county, Norway. It is located in the traditional district of Grenland. The administrative centre of the municipality is the city of Porsgrunn. Some other notable settlements in Porsgrunn include the town of Brevik and the villages of Langangen and Heistad.

Telemark is a county and a current electoral district in Norway. Telemark borders the counties of Vestfold, Buskerud, Vestland, Rogaland and Agder. In 2020, Telemark merged with the county of Vestfold to form the county of Vestfold og Telemark. On 1 January 2024, the county of Telemark was re-established after Vestfold og Telemark was divided again.