Williamsville is a village in Sangamon County, Illinois, United States. The population was 1,439 at the 2000 census, and 1,387 at a 2009 estimate. It is part of the Springfield, Illinois Metropolitan Statistical Area.
Williamsville is located at 39°57′3″N 89°33′3″W / 39.95083°N 89.55083°W / 39.95083; -89.55083 (39.950942, -89.550745).
According to the United States Census Bureau, the village has a total area of 1.2 square miles (3.2 km²), all of it land.