The American FactFinder site from the U.S. Bureau of the Census is THE place to go to get census data.
In addition to the decennial census for 2010 and 2000, American FactFinder has data from the American Community Survey, the Economic Census, and Annual Economic Surveys.
With American FactFinder you can create tables based on criteria you choose, print or download tables, and build maps showing your data.
Begin by selecting one of the options from the menu at the left:
These options are the filters you will use to build your table. Select as many options as you need. For instance, to build a table of results about the racial makeup of Galesburg, you will need to select topics from the "Race and Ethnic Groups" and also use the "Geographies" option to select a limit for Galesburg.
Each time you view the table options within a category, you need to check the box next to the data you want to view and then click the ADD button to add that data set to your table:
To limit by a geographical place, click the "Geographies" option and make selections from the lists that appear. Or, click the ADDRESS tab and enter a street address:
This is a good method to drill down to the census tract, block group or block for those smaller geographic areas you might be interested in.
When you are finished selecting data, click the CLOSE button at the top-right of the data list.
Data tables you selected will appear on the screen. Click a data table name to view, print or download. If you selected multiple data characteristics be sure to use the drop-down list to view the different data sets by characteristic, as in this example:
Browse the U.S. Census Bureau site for more data and tools.
See also the U.S. Census Bureau page on the decennial census for links to historical censuses.