Although the American Community Survey (ACS) and the Current Population Survey (CPS) produce population, demographic and housing unit estimates, the Population Estimates Program provides the official counts of the population and housing units for the nation, states, counties, cities and towns:
http://www.census.gov/popest/
The American Community Survey is an annual national survey collected monthly which provides communities with reliable and timely demographic, housing, social, and economic data every year.
American Factfinder TablesThe Current Population Survey is the largest monthly household survey conducted by the U.S. Census Bureau. This survey was designed to produce results at the national level. The prepared tables herein are at the national level.
Annual Social and Economic (ASEC) Supplement to the Current Population Survey (CPS)
Current Population Survey (CPS)