Södermanland County (Swedish: Södermanlands län, [ˈsøːdɛrmanland lɛːn]) is a county or län on the southeast coast of Sweden. In the local Sörmlandic dialects it is virtually universally shortened and pronounced as Sörmlands län, or simply Sörmland, which is the dominant pronunciation and spelling inside the county. For example, the name of the local regional council is Region Sörmland. Södermanland's capital is Nyköping and the largest settlement is Eskilstuna. In the sparsely populated interior, Katrineholm is the largest locality. In total, Södermanland has nine municipalities and about 300,000 inhabitants.
Södermanland borders the counties of Östergötland, Örebro, Västmanland, Uppsala, Stockholm and to the Baltic Sea. It holds the popular camping route called "Sörmlandsleden" which is a system of trails covering a total of approximately 100 mil (1000 km) of walking paths in Södermanland. The county has shorelines on Sweden's third and fourth largest lakes of Mälaren and Hjälmaren. There are also numerous large lakes in the Nyköpingsån river system through the west and centre of the county.