Kościerzyna County (Kashubian: Kòscérsczi kréz, Polish: powiat kościerski) is a unit of territorial administration and local government (powiat) in Pomeranian Voivodeship, northern Poland.

Its administrative seat and only town is Kościerzyna, which lies 51 kilometres (32 mi) south-west of the regional capital Gdańsk.

In the years 1920-1939 (the Second Polish Republic) and 1945-1975 (PRL) there was a Kościerzyna Land District.

In the period of September 1939 - February / March 1945, the area of the county was under German occupation.

In 1920, the county granted to Poland covered the area of 117,698 ha and was smaller than its Prussian counterpart of 6,301 ha, which left for the Free City of Gdańsk (villages of Częstocin, Trzepowo, Gromadzin, Czarna Huta, Borowina, Olszanka, Sucha Huta, and Pawłowo).