The village of Słomniki was first mentioned in 1287, as a hunting settlement in the middle of dense forests. At that time, it belonged to Cistercian monks, and was located along a merchant route from Bochnia and Wieliczka to Greater Poland. In the 13th century, Lesser Poland suffered from several Mongol raids (see Mongol invasion of Poland), in which Słomniki was also destroyed. In 1358 King Kazimierz Wielki granted Słomniki Magdeburg rights charter, and medieval style market square was fashioned, which still exists. The town developed, and several Polish rulers visited it in the 15th and 16th centuries. In 1554, Słomniki became one of main centers of Protestant Reformation, when a Calvinist temple was opened here. In 1564, the Polish Reformed Church synod took place in Słomniki. Like most towns in Lesser Poland, Słomniki was completely destroyed in the Swedish invasion of Poland, and the period of prosperity ended.