For demographic statistics, try...

Census Bureau State and County QuickFacts
QuickFacts includes commonly requested data for all states and counties, and for cities and towns with more than 25,000 people

CensusScope (Social Science Data Analysis Network)
Tool for investigating U.S. demographic trends.

County and City Data Book (GPO Access)
Comprehensive data about individual counties and cities in the United States. It includes data for all U.S. states, counties, and cities with a population of 25,000 or more. It contains additional data for places with a population of 100,000 or more.

SOCDS: State of the Cities Data Systems
A source of data about cities offered through the U.S. Department of Housing and Urban Development.

U.S. Census Bureau
Access to the wealth of data collected on people and industry.