Simplify the following text for a Grade 5 native English-speaking person.
Original: The Twenty-Second United States Census , known as Census 2000 and conducted by the Census Bureau , determined the resident population of the United States on April 1 , 2000 , to be 281,421,906 , an increase of 13.2 % over the 248,709,873 persons enumerated during the 1990 Census .
Simplified: It found that the population of the United States on April 1 , 2000 was 281,421,906 . This was an increase of 13.2 % over the 248,709,873 people counted during the 1990 Census .