High Quality Content by WIKIPEDIA articles! Wallkill is a hamlet (and census-designated place), generally identified as coterminous with ZIP code 12589, telephone exchange 895 in the 845 area code and most of the Wallkill Central School District located mostly in the eastern half of the Town of Shawangunk, Ulster County, New York but partly spilling over into adjacent regions of the Orange County towns of Newburgh and Montgomery. The population was 2,288 at the 2010 census.