Legionowo County is a unit of territorial administration and local government 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 largest town is Legionowo, which lies 22 kilometres north of Warsaw. The only other town in the county is Serock, lying 17 km north-east of Legionowo. The county covers an area of 389.86 square kilometres.