At the beginning of 1807, French troops arrived to Ostromecko. The Prussian administration was removed and the town was administrated by the Bydgoszcz Department of the Duchy of Warsaw. In addition, cavalry barracks were built in 1807-1810 in Nowy Dwór near Ostromecko, for the benefit of Polish squadron of the Duchy of Warsaw. Later, they were converted into apartments. In June 1812, Napoleon crossed the Vistula river near Ostromecko, heading for war to Russia. After the Congress of Vienna in 1815, Ostromecko and its surroundings were once again incorporated into the Kingdom of Prussia.