American FactFinder: How do I find the population of my city, town, county, or state?
From the Main Page (factfinder2.census.gov):
Note: If the city, town or county displayed is not the one you are looking for you can either modify your entry (i.e. instead of Atlanta; type Atlanta, GA) or click the link “We found more results for your geography search” located under the geography name.
Additional tools are available such as Population Finder and Quick Facts on http://www.census.gov.