For centuries, until the Partitions of Poland, Opatów was an important regional center of Lesser Poland. During an invasion of the Tartars (1502), the town was destroyed. In 1514, it was transferred to Krzysztof Szydłowiecki, who restored it, surrounded with a defensive wall, built a castle and offices for the local government, and improved the water supply to the residents. Opatów had two annual fairs and two market days a week. It was a private town, administratively located in the Sandomierz County in the Sandomierz Voivodeship in the Lesser Poland Province of the Polish Crown. In the 16th century, Opatów had a population of roughly 4,000 and was the biggest town of the province, even bigger than Sandomierz. The town was a center of political life of the Voivodeship; here General Sejmiks of the Lesser Poland Szlachta nobility took place. In 1551 Opatów burned almost completely. The great fire marked a slow decline of the town. In 1655, Opatów was destroyed in the Swedish invasion of Poland. The town also suffered during other conflicts including the Great Northern War, the Bar Confederation, the Polish–Russian War of 1792, and the Kościuszko Uprising. It belonged to a number of noble families (Tarnowski family, Ostrogski family, Lubomirski family, Potocki family, and Karski family), and remained in private hands until 1864.