Grajewo County (Polish: powiat grajewski) is a unit of territorial administration and local government (powiat) in Podlaskie Voivodeship, north-eastern Poland.

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 Grajewo, which lies 76 kilometres (47 mi) north-west of the regional capital Białystok.

The county covers an area of 967.24 square kilometres (373.5 sq mi).

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