Kętrzyn County (Polish: powiat kętrzyński) is a unit of territorial administration and local government (powiat) in Warmian-Masurian Voivodeship, northern Poland, on the border with Russia.

It came into being on January 1, 1999, as a result of the Polish local government reforms passed in 1998.

Its administrative seat and largest town is Kętrzyn (former Rastembork), which lies 88 kilometres (55 mi) north-east of the regional capital Olsztyn.

The county covers an area of 1,212.97 square kilometres (468.3 sq mi).

The county is subdivided into six gminas (one urban, two urban-rural and three rural).