Strängnäs is a municipality in central Sweden, in the county of Södermanland at Lake Mälaren. The municipality covers an area of 735.9 km². Of the total population of 29610, 14680 are male, and 14930 are female. The population density of the community is 40 inhabitants per km². An important landmark is the cathedral, Strängnäs domkyrka built around 1250.