According to Jeffrey M. Dorwart, Rio Grande was founded in the mid-nineteenth century around a country store owned by the Hildreth family. The community was originally called Hildreth for that reason.
George F. Boyer and J. Pearson Cunningham explain that, during the colonial period, Aaron Leaming, the Hildreths and the Cresses had plantations in that area. Where the King’s Highway crossed the road coming from Dennisville and Goshen a stage coach terminal was set up, and the spot became the center for trade for the local farming families. Boyer and Cunningham say that the area was known as „Leamings,“ for the prominent landholders, or as „Hildreth,“ the family who ran the local store. (p. 121-122) They continue, „The name, Rio Grande, was suggested by the seventh Aaron Leaming who thought this southern United States river had an attractive sound.“