Albeit, the list is short. A wide range of data is contained in these websites. If you are looking for just population, racial/ethnicity and gender make up, income distribution, or any combination there of or more, can easily be found. Additional websites will be added contributing to the wealth of demographic data already contained in these websites.
New York State Data Center
New York State Data Center website contains both population and economic data. Population estimates are available on the State, County, and even to the sub-county level (towns, cities, and villages). State and county estimates are available from 1990 through 1998 while the sub-county estimates are available through 1996. Economic data includes the Economic Census Data, County Business Patters, Personal Income, Business Fact Book, and various other types of data. There are links to other websites
Population Reference Bureau
Population Reference Bureau mainly provides population statistics not only within the United States, but globally. Population projections are made available until 2050. Various types of demographics are provided for all countries including percent of population in urban cities, doubling time in years, crude birth and death rates, percent of population over 65 and under 15, percent of those who are in secondary schooling, etc. Nationally speaking, resident population, median household income, ethnic/nationality break downs et al. are available
Population and Household Economic Topics
The U.S. Census provides many of the statistics on this website. The statistics are broken down into such areas as age, births, deaths, education, fertility, journey to work, language use, marital status and living arrangements, and school enrollment to name a few. Historical data for many of these areas are provided.