The region has a bit of a problem with consistency in spelling and pronunciation. The Straits, Bridge, and Island are all spelled "Mackinac" but pronounced "Mackinaw"; with the final "c" left silent. The City and the Coast Guard cutter named after it are pronounced the same way, but are also spelled that way. However, the final "c" on Fort Michilimackinac is pronounced. (The "Mich" is pronounced "Mish", just like in the name of the state; at least that's consistent.)
The regional names are consistent, considering the local Indians (various tribes) had their way of pronouncing and area, and the French and English had their way of spelling what they heard from the Indian pronounciations. Michigan remains very historic in this sense. It has kept the spellings and pronounciations as were origninally given by Indian, French and English.