The U.S. Government is the largest gatherer and publisher of statistics. You can also find statistical information from Advocacy Groups, organizations and from journal articles. Be aware of the basis of the statistics (what was gathered, by whom and when) as well the bias of who may have gathered the statistics.
Statistical Abstract of the United States - Start here. Even if you cannot find the specific data you are looking for, you can identify which agency may produce the data you need and then go to that website. Earlier Editions of Statistical Abstract of the United States are available for comparison of data .
Because of budget cutback there will be no SA after the 2011 edition. Be sure to thank your Senators & Representatives in Congress.