How many us citizens over over 18 years old?

According to U.S. census figures dated 2006, the total U.S. population is 299,398,485 of which 75.4% are 18 or older. This results in a population of approximately 225,746,457 that is 18 years or older. Source: U.S. Cencus Bureau Website: http://factfinder.census.gov/servlet/STTable?_bm=y&-geo_id=01000US&-qr_name=ACS_2006_EST_G00_S0101&-ds_name=ACS_2006_EST_G00_