Sierpc is a town in north-central Poland, in the north-west part of the Masovian Voivodeship, about 125 km northwest of Warsaw. It is the …Sierpc is a town in north-central Poland, in the north-west part of the Masovian Voivodeship, about 125 km northwest of Warsaw. It is the capital of Sierpc County. Its population is 18,368. Sierpc is a member of Cittaslow.