WASHINGTON -- Mail in today to keep census takers away.

U.S. Census Bureau officials are counting down to Friday, the day the agency switches its focus from collecting census forms to compiling lists of unresponsive households for census takers to visit starting May 1.

Households that return their questionnaires after the Friday deadline will be visited by census-takers at a higher rate than the last decennial count in 2000.

In that year, with a 72 percent national average in participation rates, the country saved $305 million in follow-up costs, according to the Census Bureau. This year, if every household mailed back its census form, taxpayers would save $1.5 billion in costs from sending census takers door-to-door to collect the same information.

As of Tuesday, only 52 counties and five cities with populations over 50,000 in the nation had either matched or exceeded their 2000 census participation rates.

Census Bureau officials commended those jurisdictions for their effort but say there's still more work to do.

"Job well done but keep it going," said Census Bureau spokeswoman Sylvia Ballinger. "Obviously, we're aiming for that 100 percent participation rate."

Census Bureau Director Robert Groves on Tuesday congratulated communities that surpassed their 2000 census figures, recognizing urban cities like Baltimore, which has exceeded its relatively low 2000 rate of 60 percent by 2 percent.

Urban areas are considered very difficult to count because of their high-density immigrant and transient populations, Ballinger said.

She said much of Baltimore's success is due to the city's leadership and census outreach program.

"We've held events, given out swag and really tried to promote the census because it is our community's resources at stake," said Kimberly Johnson, a Baltimore City's Complete Count Campaign volunteer.

Residents have a couple of options to make the Friday deadline and avoid census takers arriving at their doors.

Residents can drop off completed forms at any one of the several census questionnaire assistance centers located throughout the states.

Location and hours of operation can be found at 2010.census.gov.

From April 12 to April 21, residents can call the census telephone questionnaire assistance center and answer census questions over the phone. Lines are open from 8 a.m. to 9 p.m., seven days a week.