Why is Pierre SD, pronounced "Peer"

Was it ever pronounced as “Pee-air” or was the pronunciation changed over time?

No, it’s still pronounced ‘pee-AIR’.

Wikipedia backs up the OP.

Pierre, South Dakota, is “Peer” to natives.

See also VerSALES (Versailles), Kentucky; Dez Planes (Des Plaines), KAYro (Cairo) and MYlin (Milan), Illinois; Byoona (Buena) Vista County, Iowa; ValpaRAYzo (Valparaiso), Indiana…

…Bellefontaine, OH, charmingly referred to as Belluhfont…

I heard the mayor of Lima, Ohio on NPR a couple of weeks ago. He explained the origin of the name (i.e., why they named it Lima), which was cool. But I wasn’t really satisfied by his explanation of the pronunciation. Basically it sounded like ‘The town was named after Lima, Peru; but we pronounce it “LIE-ma”.’ He didn’t actually say why.

It’s just an example of the Anglicization of foreign names. It’s an adoption process common to all languages.

Hurricane, WV is Hurr-uh-kun to locals. Pronouncing it like the storm is unforgivable.

I’m a native West-by-God-Virginian, and I approve of this message. Jiminator, in fact, may be a bit generous in including the middle syllable. What I always heard was more like Hurr-kun.

But now I live in Ohio, where we have BER-lin, the aforementioned LYE-ma, and my favorite, MANT-a-way (Mantua), which is pronounced thus despite the sign at the town limits declaring that it was named for the “famous Italian city.”

Ohio also has, or at least had at one time, a Greenwich pronounced like it looks. It might be “Gren Itch”, England, and “Gren Itch Village” in NY, but it’s “Green Witch”, Ohio.

Not invariably, at least not in the US.

Although there are plenty of places when the pronunciation has been altered from the more famous version (many quoted above, or like Connecticut’s Thames river, with New London on it, that’s not pronounced “tems”, but with a “soft” “the” and a long “A”), there are places where the original pronunciation is preserved and cherished, like New Orleans, which natives keep closer to the French “new OR-l’ns” than to “New or-LEENS”, or Baton Rouge, which is “ba-TOHN ROOZH” rather than, say, “BAY-ton ROOG”. Or a LOT of Spanish names in the southwest, like La Jolla, which is invatriably pronounced “La HOYA”.)

Real old-timers pronounce it “Grinnidge”.

How is the storm pronounced in American English? “Hurr-uh-kun” is a close approximation to the British pronunciation - maybe “Hurr-ih-kun” would be closer.

Hur-i-cayn

It may be Bo-ga-TAH, Columbia but it’s Buh-GO-tuh, Texas.

The natives of Pierre, S.D. will regard you with a double :dubious: if you pronounce it as anything other than “Peer”.

On a similar note, Rio Grande, Ohio is (for some reason) pronounced “Rye-o Grand”. This could be important if you make the pilgrimage there to see the Bob Evans Farm, where the tradition of unhealthy lard-based eatin’ was born.

“…sit at the reconstructed counter of the original Steak House owned by Bob Evans, see life-size models of Bob and Jewell Evans, filming their television commercials in their original kitchen”

I know what I’m doing this summer!

To actually respond to the OP regarding why the city is pornounced that way, I would imagine it was the large Scandnavian population in the state as opposed to a virtually nonexistent French population who would have gone with the more francaphone pronunciation.

To add three more pronunciation differences to the growing list.

Montrose, Colorado is pronounced “Mont’ rose” by the locals as opposed to the more usual “Mon trose’”. They joke that they pronounce it that way to catch the outsiders trying to pass themselves off as locals.

Boise City, Oklahoma residents pronounces the first word in their name not like the capital of Idaho but rather in a way that rhymes with the second word in the British car, Rolls Royce. All non-Panhandle people mess that one up.

A number of communities in the U.S. don’t pronounce Madrid the same way the Spanish do as “Ma drid’”. The fault line, the community in the midwest and even the town in New Mexico, are pronounced “Mad’ rid”

If ever you go to Moscow, Idaho, don’t pronounce the name like the capital of Russia, but instead say Mos - co (co as in the first syllable of company)

Except in Hartford, Hereford and Hampshire, of course…

Super-slight nitpick:

“Batten Roozh” is the native pronunciation. “Baton” rhymes with “Patton”, not with “soupçon”.