Coal has been part of America's past for just about as long as there's been an America.
It was the energy source du jour for the Industrial Revolution. In the 1300s, some Native Americans used it for cooking fuel. And the first North American coal deposits may even predate the dinosaurs!
But if we're talking America the post-colonial country, then nowhere was it more important than in the Appalachian Mountains, in places like Pennsylvania, Kentucky, Tennessee, and West Virginia.