Ciechanów Land (Polish: ziemia ciechanowska), named after the town of Ciechanów was an administrative unit (ziemia) of both the Kingdom of Poland and the Polish–Lithuanian Commonwealth. Divided into three counties, it belonged to Masovian Voivodeship. The Land of Ciechanów was densely populated, with poor szlachtas making up to 30% of total population. Local residents colonized the neighboring lands of Podlasie, Lithuania, Prussia (see Masurians), Volhynia and Pomerelia.