In 1795 Prussia annexed Augustów in the Third Partition of Poland. In 1807, it became part of the Duchy of Warsaw, followed by incorporation into the Kingdom of Poland in 1815. It was made a county seat in 1842. Following Russia's full annexation of the Polish kingdom in the 1860s, it was administered from Suwałki. With a population around 9400 (), it carried a large trade in cattle and horses, and manufactured linen and huckaback. Its canal connects the Vistula and Neman rivers and the railway reached the town in 1899, when its population was around 12,800.