Every 10 years, the United States counts its residents -- and it's a really big job. A decade ago, the number was 281,421,906. Now it's time to count again, so this month every home in the country will get a form asking how many people live there and other basic information.

This giant counting exercise is called the U.S. Census. It doesn't just produce numbers; the information gathered is a snapshot of America, telling us who we are and where we come from. It shows us how America has changed over time.

And it gives you something to compare yourself with. For example, the average U.S. family has 3.2 people. Is yours bigger or smaller than that?

The government also uses the information from the census to figure out how much money is needed for things such as hospitals, schools, roads and emergency services. Census data are also used to draw district lines for members of Congress, which can affect how many representatives each state has in Congress.

So the census is really important -- and cool. If you see the form lying around, remind your parents to fill it out.

FROM THE 2000 CENSUS

• Total U.S. population: 281.4 million

• Number of children under age 18: 72.3 million

• State with the most people: California (33.9 million)

• State with the fewest people: Wyoming (493,782)

• State with the youngest residents: Utah (median age 27.1 years)

• State with the oldest residents: Florida (median age: 38.7 years)

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