Fountain Green is an unincorporated community located about eleven miles northeast of Carthage, Illinois, United States in Fountain Green Township, Hancock County, Illinois.

One of the earliest settlers in this area was Mordecai Lincoln, who prior to 1830 led a group from Kentucky in an attempt to establish a Catholic settlement in this part of Illinois, presaging by several years the Mormon settlement in nearby Nauvoo.

The Catholic settlement foundered, in part because of the difficulty in obtaining a parish priest.

An Irish Protestant church (Calvinist) was soon established in Fountain Green, attracting members from the earlier groups.

This seems to have been a local manifestation of the general movement in the North away from the Baptist church, which, in the 1850s, supported slavery.