In Illinois Casimir Pulaski Day, first Monday in March (since 1977).
He was "a
Revolutionary War cavalry officer born in
Poland as Kazimierz Pułaski. He is praised for his contributions to the
U.S. military in the
American Revolution and known as "the father of the American cavalry". " (Wikipedia)
At first all Illinois schools had the day off (I believe), but in the past some districts (ours included) have petitioned the state to not close on the holiday.
My kids' district did have it off about 10 years ago because the district forgot to file their petition.
I believe there were some actual celebrations in the Chicago area (large Polish population), but not really anywhere else. Just a day the State offices and schools were closed.