Hallstahammar is a locality and the seat of Hallstahammar Municipality in Västmanland County, Sweden with 10,478 inhabitants in 2010. The King Gustav Vasa built Strömsholm Castle along the lake about 1558. Its current appearance goes back to the 1680s. Today it hosts an interesting museum.
The town Hallstahammar traces its history to 1628 when the first smithy was built. In 1795 the Strömsholm Canal was inaugurated which enhanced goods transports. The town became a centre for transportation and commerce. In the 1930s it was shaped as a typical Swedish industrial town with close ties to the engineering industry. From the 1970s on, however, that industry has gradually lost its strong significance.