Nidzica County (Polish: powiat nidzicki) 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 only town is Nidzica, which lies 48 kilometres (30 mi) south of the regional capital Olsztyn.
The county covers an area of 960.7 square kilometres (370.9 sq mi). As of 2006 its total population is 33,955, out of which the population of Nidzica is 14,761 and the rural population is 19,194.
The county's population has stagnated and remained the same for the past four decades, never surpassing the 35300 mark.
In 1825 Nidzica County (Kreis Neidenburg) had 29617 inhabitants, including by mother tongue: 27467 (~93%) Polish and 2149 (~7%) German.
Nidzica County is bordered by Olsztyn County to the north, Szczytno County to the east, Przasnysz County to the south-east, Mława County to the south, Działdowo County to the south-west and Ostróda County to the north-west.
The county is subdivided into four gminas (one urban-rural and three rural). These are listed in the following table, in descending order of population.