Back in 1849, Franklin had a circulating library. But it wasn't until 1926 that the idea of a demonstration parish library system was introduced to Franklin residents by Essae Culver, Executive Secretary of the Louisiana Library Commission. It took another 23 years, until 1949, for the police jury to approve the establishment of a demonstration library in St. Mary Parish. The state provided $50,000 for the library, along with trained librarians and a bookmobile, while the police jury contributed $5,000 towards funding. The main library was located in Franklin, the parish seat. Franklin, Patterson, and Berwick voted in favor of the parish library system, but Morgan City chose to maintain its own established municipal library separate from the parish system. The St. Mary Parish library Franklin branch and headquarters opened in October 1953, and the first librarian was Ann Kersieck of Abbeville, a graduate of the LSU Library School. The system started with three branches: Franklin, Berwick, and a segregated branch in Franklin, named after Nobel Peace Prize winner Ralph Bunche. Marion Chube was the assistant librarian at the Bunche Branch. It was located at 406 Second Street, later relocated to the corner of Fifth and Willow Street. Yvonne Frentz was the librarian at the Berwick branch. It was located at 357 Lima Street.

The St. Mary Parish Library headquarters was first located at 509 Willow Street, with the Franklin branch at 510 First Street. However, in 1957, a brand new library and Health Unit building was constructed at the intersection of Iberia and Perret St. Later, in 1966, the building was refurbished with the help of funding from the federal Library Services and Construction Act. The renovations included a two-story 9600 square foot addition, a 100-person capacity meeting room, and a bookmobile garage. 

The Franklin Branch was renamed to the Alex P. Allain Memorial Branch in 1994. Alex P. Allain, a sugar cane planter and lawyer from west St. Mary Parish, was born on June 27, 1920 and passed away on January 5, 1994. He was a founding member of the St. Mary Parish Library Board and served for more than 40 years. He strongly believed in First Amendment rights for libraries and played a key role in establishing the American Library Association Office for Intellectual Freedom. Additionally, he founded the Freedom to Read Foundation and was awarded a lifetime membership to the American Library Association for his contributions to the field. The award read, in part, "The American Library Association extends its highest award of Honorary Membership to Alex P. Allain. Recognizing that there is no liberty without freedom of the mind, you have devoted your singular talents and boundless energies to the realization of intellectual freedom in library service in America. Sounding the clarion call for an effective organization for defending the Library Bill of Rights, your leadership inspired the establishment of the Freedom to Read Foundation; in the enthusiasm of your service as a trustee and as first president of the foundation, you have set a standard for us to meet."

Currently, the library can be found at 206 Iberia Street.