In medieval written sources, Płońsk occurs as Plonz, Plonsko, Plonysko, in Plonszko, Ploń, in Ploniska, and in Plonsk. Currently, there are two versions of the origin of the town’s name. According to the first one, the name is of topographic character and it origins from the term ”płona” or ”płonia” meaning swift, deep fragments of rivers that do not freeze in the winter. According to the second one, the town was a place of cult of the Slavic god Płona and was named after him.