Unionville is a census-designated place located in Center Township, Butler County, in the U.S. state of Pennsylvania. As of the 2010 census, the population was 962. Unionville is located in the northwestern corner of Center Township and is bordered to the southwest by the Shanor-Northvue CDP, to the north by Clay Township and to the west by Franklin Township. Pennsylvania Route 8 passes through the community, leading south 6 miles to Butler, the county seat, and north 14 miles to Harrisville.