From the New England Carnegies site:
A Brief History of the Building
1915: Andrew Carnegie gave $25,000 to the town to build the library.
1916: The library opened on October 25. 
The original West Springfield Public Library was founded in 1854 and housed in the Town Hall. In 1913 the Town Hall library facility had reached its capacity. In 1914, with a $25,000 grant from Andrew Carnegie, the town was able to construct a new fully equipped building. On October 25, 1916, the new library was opened on the west corner of Park and Elm Streets. It was designed by Edward L. Tilton in the Italian Renaissance Revival Style. 
From the website of Centerbrook Architects and Planners:
Centerbrook, in collaboration with Caolo & Bieniek Associates of Chicopee MA, and Adams & Smith Architects of Swampscott, MA, have designed a 32,000-square-foot addition to the West Springfield Public Library. The project entailed removal of two mid-20th century additions from the original 1916 Italianate Revival building, a "Carnegie Library" funded by the renowned industrialist. The restored Carnegie building will serve as a gracious reading room.
A new wedge-shaped, high-ceilinged public welcoming lobby links the ‘Carnegie Room’ to the two-story addition that houses the majority of the library’s services: the main collection with nooks for quiet reading and study, dedicated children’s and young adult rooms, a 150-seat community meeting room, a local history room, a language education room, a computer lab, and ample seating for library patrons. 
According to the architectural firm tasked with the remodeling, the library was dedicated (not opened) on April 2, 2016 . I have not found any corroborating evidence for this claim.