The US Census Bureau has multiple sets of data that it releases that deal with the population and its characteristics.
First there is the 2010 census, including the Redistricting and the Summary File 1. These data sets are the official counts of the US population and are required in the constitution as the charge for the USCB. These counts are used for the apportionment of congressional and legislative districts.
Secondly there are the Annual Estimates, these are the official numbers that the USCB releases for the years between censuses. They include population totals and then breakouts by age, race, Hispanic origin, and gender. The USCB also only releases these at the county level and we have modeled them down to smaller geographies and have also modeled many other variables to make the data set more robust and useful.
Third there is the American Community Survey. The ACS was designed to measure the changing social and economic characteristics of the US population but not to provide official counts. Among other things the ACS is collected over multiple years and then merged into a common file.
2010 Summary File 1 in 2000 Boundaries - this is the exact same data as the official 2010 Summary File 1 census data set. Except that we have crosswalked it to the 2000 census geographic boundaries. This allows the user to then compare the 2010 numbers to the 2000 census numbers as well as to compare it to other normalized products that are in the 2000 boundaries.