I'm not really sure whether these are "colloquialisms", as specified by Kat, but they are speech peculiarities, and might be interesting.

Here in Indiana we have a number of place names that are familiar, but "different".

Milan, a town in southern Indiana, is not pronounced like its Italian forebear. It's "MY-luhn".    Milan, Michigan has this same distinction.

Lafayette is SOMETIMES pronounced like the famous Marquis, but it's not too unusual to hear it pronounced "Lay-fee-ette". Or even "La-FAY-ette".

Orleans, in Orleans County, Indiana, is not pronounced like the second word in "New OR-luhns". It's definitely, and always, "Or-LEENS".

Terre Haute, Indiana (meaning "high ground"), ought to and many times is pronounced "TAIR-uh Hote", but it often loses the second syllable of "Terre" to become "Tair Hote". And worse, "Tair Hut". Or, for conscious humor, "Terrible Hut".

Then (not a pronunciation matter, but of interest), there's a "Needmore, Indiana". In fact there's another one of that name in the state. No, there are actually two more, for a total of three Needmores in Indiana. I guess someone thought we needed more or them.