Ciechanów, city, Mazowieckie województwo (province), east-central Poland. It is located in the Ciechanów Highlands on the Łydynia waterway, the Wkra River inlet, and the Warsaw-Gdańsk railway line, in a fertile agricultural area that produces wheat, rye, sugar beets, and potatoes. A walled city since the 11th century, it was one of the Christian Polish communities placed under the protection of the Teutonic Knights of Mazovia early in the 13th century. Pop. (2011) 45,481.