Södermanland, län (county) of east-central Sweden. It lies along the Baltic Sea near Stockholm and is bounded by Lake Mälar and Lake Hjälmar. Its area consists of most of the traditional landskap (province) of Södermanland. It is a lowland region that has many small lakes and fertile soils. Grain and fruit are grown, and there is some stock raising and dairying. Industries include iron mining, woodworking, and papermaking. The län gains importance from the Södertälje Canal in the east, which links Lake Mälar with the Baltic. Urban centres include Nyköping, the capital; Eskilstuna, known for its engineering industries; Katrineholm, a railway junction and industrial town; and the Baltic port of Oxelösund, which is the export harbour for Bergslagen iron and steel. Area 2,551 square miles (6,607 square km). Pop. (2005 est.) 261,070.