Ostrołęka (ôstrôwĕnˈkä) [key], Rus. Ostrolenka, town (1993 est. pop. 52,400), Mazowieckie prov., NE Poland, on the Narew River. It is a railway junction and a manufacturing center where pulp and paper, lumber, and foodstuffs are produced. Chartered in 1427, it passed to Prussia in 1795 and to Russia in 1815. It reverted to Poland in 1920. The town has several churches built in the 14th and 17th cent.