W. P. Irwin Bank Building is a historic bank building located at Rensselaer in Rensselaer County, New York. It was originally built in 1873 and is a 2-story, rectangular flat-roofed, masonry structure on a stone foundation. A 1+1⁄2-story, four-bay flat-roofed brick rear wing was added in 1905. The building exhibits a number of Gothic Revival details.