Sierpc County (Polish: powiat sierpecki) is a unit of territorial administration and local government (powiat) in Masovian Voivodeship, east-central Poland.

It came into being on 1 January 1999 as a result of the Polish local government reforms passed in 1998.

Its administrative seat and only town is Sierpc, which lies 117 kilometres (73 mi) north-west of Warsaw.

The county covers an area of 852.89 square kilometres (329.3 sq mi).

These are listed in the following table, in descending order of population.