Nidzica is a town in the Warmian-Masurian Voivodeship of Poland, lying between Olsztyn and Mława, in Masuria. The capital of Nidzica Coun…Nidzica is a town in the Warmian-Masurian Voivodeship of Poland, lying between Olsztyn and Mława, in Masuria. The capital of Nidzica County, its population in 2017 was 13,872.