The United States census of 2010 was the twenty-third 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. Introduction As required by the United States Constitution, the U.S. census has been conducted every 10 years since 1790. The 2000 U.S. census was the previous census completed. Participation in the U.S. census is required by law of persons living in the United States in Title 13 of the United States Code. On January 25, 2010, Census Bureau Director Robert Groves personally inaugurated the 2010 census enumeration by counting World War II veteran Clifton Jackson, a resident of Noorvik, Alaska. More than 120 million census forms were delivered by the U.S. Post Office beginning March 15, 2010. The number of forms mailed out or hand-delivered by the Census Bureau was approximately 134 million on April 1, 2010. Although the questionnaire used April 1, 2010 as the reference date as to where a person was living, an insert dated March 15, 2010 included the following printed in bold type: "Please complete and mail back the enclosed census form today." The 2010 census national mail participation rate was 74%. From April through July 2010, census takers visited households that did not return a form, an operation called "non-response follow-up" (NRFU). In December 2010, the U.S. Census Bureau delivered population information to the U.S. president for apportionment, and later in March 2011, complete redistricting data was delivered to states. Personally identifiable information will be available in 2082. Major changes The Census Bureau did not use a long form for the 2010 census. In several previous censuses, one in six households received this long form, which asked for detailed social and economic information. The 2010 census used only a short form asking ten basic questions: How many people were living or staying in this house, apartment, or mobile home on April 1, 2010?