If you don't mail back your 2010 census form soon, someone may come a-knockin' on your door next month.

Maybe it will be Cara Herbst. The 24-year-old actress spent a sunny afternoon last week hunched over logic and multiplication problems down in the basement of the Brooklyn Public Library's Williamsburg branch, trying to get a part-time job as a census taker.

"I sold candy as a little kid sometimes, so I think it will be like that," said Herbst, who lives on the upper East Side.

The official job title is "enumerator," and it entails going to the homes of people who didn't send back their census form to explain what the once-a-decade tally means and record responses to the Census Bureau's 10 questions.

"It's a short-term gig that pays well," Herbst said. "It's a way to raise some money and pursue my own projects."

Like Herbst, thousands of New Yorkers are looking to the census for some extra cash. The bureau has hired 20,000 people from the New York area in the past year for temporary jobs that pay from $14.75 to $20.25 an hour.

Nationwide, census hiring was so massive that it accounted for nearly one-third of the jobs added in March, the U.S. Department of Labor says.

And the bureau is still bringing in new people - the exact number of census takers will depend on how many people send back their forms before the April 16 deadline. Of course, the census folks hope they won't need to hire as many people as they did 10 years ago.

Officials sent out a second census form last week to neighborhoods around the country where response was low in 2000 because it would save taxpayers $1.5 billion if everyone mailed in their answers.

The bureau is still recruiting in New York, which has only just hit the halfway mark - 50% of households had mailed back their forms by Thursday.

Job hunters can call the census hotline at (866) 861-2010 to set up a time and place to take the exam, which involves 28 multiple choice questions that test skills like alphabetizing, adding and logic. There's a practice version online at 2010censusjobs.gov.

"It was pretty easy," said Jonathan DeSantos, 19, from Williamsburg, after finishing the half-hour exam last week. He's really hoping he gets to carry a census clipboard, since he's been job-hunting for the past three months.

"I need money. I'm going to college in September," said DeSantos, who will be a freshman at Brooklyn College.

Marie Ciceron, a 32-year-old home health aide from East Flatbush, is also vying for a census taker job and took the test at the main branch of the Brooklyn Public Library in Grand Army Plaza. She thinks it would fit her personality well. "I'm not shy," she said. "It's a part-time job where you can actually help your community."