Named for the campsite of a group of Ex-"Mormons" who had separated from the main church group in Illinois The main church was known as the "Church of Jesus Christ of Latter-Day Saints". The main body of this church continued on from Illinois to settle in Utah.  Often all of them were mislabeled 'Mormons', a rude name enemies called them.

Many splinter groups formed and drifted elsewhere and formed their own churches. 
This one that came through Grayson County, was led by Lyman Wight who came into Grayson County in the fall of 1845 and wintered in the "Mormon" grove. From there they moved southwest into the Texas Hill Country to Gillespie County.

Mormon Grove was where they camped that winter and since it was an isolated spot and had little water resources, locals made up all kinds of stories about what they could be doing there. All kinds of rumors started and they place got it's name!