Mackinac Island is pronounced Mackinaw.
Kingman, KS.
You look at it and think, how many ways can that be pronounced? It’s king-man!
Uh-uh. It’s kay-men. Like the islands.
(My dad grew up there, which is the only reason I know.)
In Ireland we have a few. They include:
Muckanaghederdauhaulia, Co. Galway
Graiguenamanagh, Co. Kilkenny
Youghal, Co. Cork
I tried to learn Gaelic in the '80s. Aside from that I joined in during the second ‘year’, it had too many consonants.
South Louisiana offers some fun-looking names, but (outside of New Orleans, Johnny), most of them aren’t really that hard, despite the Cajun spellings. North Louisiana, on the other hand, offers this prize:
Natchitoches. Pronounced NAK-ə-təsh.
That’s as opposed to Nacogdoches, TX (NAK-ə-DOH-chiss), about 100 miles away, which is–as I understand it–named after the same tribe. The French were worse at transliterating Caddo names than the Spanish, I guess.
Here in Georgia, we like to name towns after places we’ve never been, and damn their pronunciation!
Lafayette is le-FAY-ut
Cairo is KAY-roh
Vienna is VIE-EE-nuh
Albany is All-benny
Louisville is Loo-iss-ville.
Houston County and Houston Street in Savannah are pronounced properly, however - House-ton. Not like that Johnny-Come-Lately burg in Texas! 
But Poulan isn’t pronounced like the chain saw - it’s “Poland.” And just down the road a piece from Ty Ty. (Tie-tie. Named for a type of tree.)
And Talliaferro County, the Altamaha River, and the Gordonia Alatamaha State Park are good ways to weed out the locals from the imports around here.
My favorite mispronunciations are for Vidalia (like the onion,) Uvalda, and Ludowici (an infamous speed trap in the not-too-distant past.) Many people seem to want to “gussy them up,” giving them a Continental flair: “Vi-dahl-yuh,” “You-vahl-duh,” and “Loo-de-wee-chee.” Nope. “Vie-dail-yuh,” (if your from the surrounding areas. If you’re local, it’s more like “Vie-day-yuh.”) “You-vall-duh,” and “Loo-duh-wiss-ee.” Dacula doesn’t rhyme with the famous Count, it’s Da-KYOO-luh.
Havre, Montana.
Pronounced /ˈHævər/, like “have 'er” as in “you can have 'er”.
That’s what I came to post! I really did not expect anyone to beat me to it. I’ve met Texans who haven’t heard of Corpus, let alone any of the little nearby towns.
You are a very surprising gentleman, mister.
I lived for a few years in Stouffville, Ontario.
It’s pronounced STOW-ville. The “fs” are silent.
I was always surprised at the people who tried to pronounce the “fs” along with the “v”:
STOUFF-ville
STUFF-ville
No, it’s pretty easy. STOW-ville. That’s all there is to it.
I lived for years near a small town named Mantua. The sign at the town limits state that it was named after the famous Italian city. It’s pronounced Manna-way.
A few counties over, Russia Township is pronounced ROOSH-ee.
We have that in Ohio, except for some reason we’ve decided it’s pronounced bell-FOUNTain.
I grew up in the tiny village of Karitane. Nearby was the village of Waikouaiti, which for a long time everyone who lived in the area mispronounced, until we (as a Nation) started to respect the Maori language for a change.
They are pronounced thus:
Karitane: Ka - ruh - TAH - nee
Waikouaiti: WY - ko - WY - tee
I got the first one right. I just got up though, and haven’t even had one cuppa joe, so I couldn’t get my eyes to focus enough on the second one.
Portsmouth NH - it’s ports-muth, not ports-mouth
Haverhill, MA - hav-rel, not haver-hill
Barre, VT - bar, not barry
Is it true that people in the Washington, DC area call Maryland ‘Merlin’?
I grew up in Louisville Kentucky, then moved back “home” to Minnesota when I was eleven. I do a pretty good job of hiding the drawl most of the time, but it comes out if I slow my speech or spend any time South of Des Moines (Da Moin). And I simply CANNOT bring myself to say Looey ville. Its Lou-a-vul.
Minnesota has its share of misprounced French and/or Indian towns. It doesn’t seem to be as bad as Wisconsin.
There’s a town near me that separates the locals from the come-latelys: Leicester. The locals pronounce it “Lester.” The come-latelys are all over the place, but most call it “LEE sester.”
Near Charlotte there’s Waxhaw and Monroe. The local pronunciation is “WAXAW,” all one syllable with the “h” elided out and “MON roe” with the o pronoucned like the word “on”. Of course there are so many transplants in Charlotte now that most people pronounce them “WAX-haw” and “Mun-ROE.”
Many people are aware that Cairo (at least in NY) is not pronounced KI=ro (Is the one in Egypt pronounced that way either?) but saying Kay-ro still marks you as an outsider. Locals say Care-o.
–including Versailles (“Ver-Sails,” equal emphasis to my ear).
In one MO town there is a Worchester Street generally pronounced Wooster but (at least some years ago) spelled about 4 different ways on street signs.
In New York on Long island is Islip which only yesterday I learned is pronounced “I-Slip,” I have no idea of syllable emphasis.
I had always pronounced Cayman, as in Cayman Islands like Kay-Min, until I found out the way the locals pronounce it is Kay-Man.