What Illinois town was the first Mormon Temple constructed?

The first temple in Illinois was in Nauvoo, which was built in the 1840's. It was destroyed by fire in 1848 and rebuilt in 2002. There is also a temple near Chicago. You can read about the Navuoo temple here:

www.ldschurchtemples.com/nauvoo and the Chicago temple here:

www.ldschurchtemples.com/chicago