A gift to the Town of Johnston by Ralph S. Mohr and named for his late wife, the town's only library was completed in 1961. Originally placed on school property, the library became a municipal service following the passage of the Library Services and Technology Act of 1964. 

Two additions, in 1967 and 1989, expanded the building's space to 4,200 square feet, though it was still among the smallest in Rhode Island until the opening of a new library building on April 9, 2011.

Mohr Library currently serves 7,800 visitors per month with nine full-time and nine part-time staffers. Jon Anderson has been the library's Director since 2003.