Łomża County (Polish: powiat łomżyński) is a unit of territorial administration and local government (powiat) in Podlaskie Voivodeship, north-eastern Poland.

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

The county covers an area of 1,353.93 square kilometres (522.8 sq mi).

The county is subdivided into nine gminas (two urban-rural and seven rural).

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