Overview of the Czech area...

I remember as a wee kid, my uncles playing the accordion, so the examples here especially attracted me.

Chromatika (button accordion)
Prague, 20th c.
Antonin Hlaváček, maker
Ex. Walter J. Endmann Collection
Musical Instrument Museum #2009.65.23???

Heligonka (button accordion)
Louny, Ústí nad Labem Region, c. 1925
Josef Hlaváček, maker

Named after the heligon due to its similar bass sound.
Musical Instrument Museum #2009.68.22.1

Heligonka (button accordion) Probably Bohemia, early-to-mid 20th c. MIM, #???

I don't think this accordion was part of the Czech collection, I don't see it in the "overview" photos, but I didn't capture all of the area. I might have just taken its photo because it is so beautiful.

"Organetta III" model (piano accordion)
Trossingen, Baden-Württemberg, Germany, 1934
Matth. Hohner AG, maker
The curved fingerboard facilitates a more natural movement of the right hand.
Ex. Walter J. Endmann Collection
MIM, #2010.165.29

Wikipedia says "German and Czech immigrants arrived with accordions (usually button boxes)". The Czechs would play the polkas they learned in their homeland. There is also a dance done to Polka music. "Polka is defined as a vivacious couple dance of Bohemian origin in duple time; was a basic pattern of hop-step-close-step; a lively Bohemian dance tune in 2/4 time. The polka was originally a Czech peasant dance, developed in Eastern Bohemia (now part of Czechoslovakia)." (Editor's note, some time has gone by since the source page was written. Eastern Bohemia is now part of the Czech Republic)

"The dance was first introduced into the ballrooms of Prague in 1835. The name of the dance (pulka) is Czech for "half-step", referring to the rapid shift from one foot to the other." Eventually, it spread to the States, where "Breiter's band composed a new polka for the occasion of the 1849 [Philadelphia] Assembly."
(Source: History of Dance, Polka page)