In the book, the author repeatedly says 'Trapingis County' but the story takes place in Louisiana and in that state, and only in that state, counties are known as parishes.
Even if the book were set in Louisiana, I'm not sure this could be considered a slip-up. Stephen King is well-known for creating places that don't exist.
MOST of his books take place in Maine, but not all of them. The Shining for example takes place in Colorado.
The book took place in Georgia, the movie took place in Louisiana.
Actually, both the book and the movie are set in Louisiana (which has parishes and not counties). Cold Mountain is loosely based on Angola (Louisiana State Penitentiary) which was notorious for its mistreatment of prisoners.
Georgia Pines is the name of the nursing home Paul Edgecombe lives in at the end of his life, but the books itself is set in Louisiana. There aren't a lot of Cajuns in Georgia, nor is Baton Rouge in Georgia.