Polka dots are, perhaps unsurprisingly, named for the dance called the polka. According to the Online Etymology Dictionary

polka dot — 1874, from polka (n.) + (n.). Named for the dance, for no reason except its popularity, which led to many contemporary products and fashions taking the name.

polka — 1844, from French polka, German Polka, probably from Czech polka, the dance, literally “Polish woman” (Polish Polka), fem. of Polak “a Pole.” The word might also be an alteration of Czech pulka half, for the half-steps of Bohemian peasant dances. Or it could be a merger of the two. The dance was in vogue first in Prague, 1835, it reached London by the spring of 1842.

Una breve storia della Polka Dots

La storia della Polka Dots in foto