Short Answer:
Gibson electric guitars are produced in their flagship factory in Nashville, Tennessee. Gibson acoustic guitars are produced in Gibson's dedicated acoustic guitar factory in Bozeman, Montana.
Long Answer:
You don't get to your place as one of America's premier electric guitar brands without some American heritage. While the Gibson name has moved around the United States once or twice, currently, their production of mainline Gibson electric guitars resides in Nashville, Tennessee. The other place Gibson factories is most commonly associated with, Kalamazoo, Michigan, was left after the company relocated in the mid-1980s.
While American-made Gibson-brand guitars have been produced in Nashville, Tennessee for a couple decades now, Gibson's production has expanded with other brands including Gibson Custom Shop and Gibson Acoustic. Gibson's acoustic guitar production was moved to Bozeman, Montana in 1988. Bozeman, chosen for its regular annual climate and humidity, made for an ideal location for the production of acoustic guitars.
However you get your hands on a Gibson guitar, you're working with generations of fine American craftsmanship in the works.