The United States Census of 2010 is the twenty-third and most recent United States national census. National Census Day, the reference day used for the census, was April 1, 2010. The census was taken via mail-in citizen self-reporting, with enumerators serving to spot-check randomly selected neighborhoods and communities. As part of a drive to increase the count's accuracy, 635,000 temporary enumerators were hired. The population of the United States was counted as 308,745,538, a 9.7% increase from the 2000 Census. This was the first census in which all states recorded a population of over half a million people as well as the first in which all 100 largest cities recorded populations of over 200,000.