These guys probably have something you could use.
http://eire.census.gov/popest/data/cities.php
"The Population Estimates Program publishes total population estimates for incorporated places and county subdivisions. Incorporated places include cities, towns, boroughs, and villages (depending on the state). County subdivisions cover all governmentally functioning minor civil divisions. The reference date for place estimates is July 1. There are about 41,000 places in the tables for the whole U.S.; you may instead choose to view places state by state. "