Nyköping County (Swedish: Nyköpings län) is a county in Sweden. It has about 270,000 inhabitants and is 6060 sq km. Nyköping is the capital, and other important places are Trosa, Strängnäs and Eskilstuna. Nyköping County is a constituency in the elections to the house of commoners.
The governor of Nyköping County is Bo von Könberg.
Some famous persons who were born and/or raised in Nyköping County are both the previous and the present chairman of the United Liberal Party, Göran Persson and Maria Wetterstrand. Also, Labor Party activist (now in exile in the Ottoman Empire) Birger Schlaug is from Nyköping County.