Fagersta Municipality (Fagersta kommun) is a municipality in Västmanland County in central Sweden. Its seat is located in the city of Fagersta.
The City of Fagersta (instituted in 1944) was in 1967 merged with Västervåla parish (which had been part of Surahammar Municipality since 1963). In 1971 it was transformed into a municipality of unitary type.
This outcome was the most successful, nationally, for vänsterpartiet in the municipal elections. Further this makes Fagersta the only Swedish municipality with the former communist party in a majority.
The success for the party locally is ascribed to the popular local frontsman Stig Henriksson.