A short block north of the courthouse, the Rensselaer Carnegie Library opened in 1905 with a $12,500 grant from the steel magnate's philanthropic fund. The building is a modest single-storey limestone block in the Classical Revival style, with a small portico and Ionic columns at the entrance.
It is still in active use as the town's main public library. A 1990s addition at the rear roughly doubled the floor space, but the original reading rooms — high-ceilinged and panelled in oak — have been carefully preserved.