Koszajec [kɔˈʂajɛt͡s] is a village in the administrative district of Gmina Brwinów, within Pruszków County, Masovian Voivodeship, in east-central Poland. It lies approximately 4 kilometres (2 mi) north-east of Brwinów, 4 km (2 mi) west of Pruszków, and 18 km (11 mi) west of Warsaw.