Działdowo County (Polish: powiat działdowski) is a unit of territorial administration and local government (powiat) in Warmian-Masurian Voivodeship, northern 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 Działdowo, which lies 65 kilometres (40 mi) south of the regional capital Olsztyn.

The only other town in the county is Lidzbark, lying 25 km (16 mi) west of Działdowo.

The county covers an area of 953.18 square kilometres (368.0 sq mi).