The 2020 Census is almost six years away, but for 190,000 households in the greater Washington area, Tuesdaywas Census Day.

The Census Bureau is using nearly one in three households in the District and Montgomery County as test subjects so it can figure out how best to use technologies in future census counts. With July 1 as a fixed reference date, residents were asked to go online to answer a short series of questions about their race, gender, age, household size and whether they’re renters or homeowners.

This is the first large-scale field test designed to see how the internet and mobile phones can be employed in ways that could shave as much as $5 billion off the tab for the decennial count in 2020. The Census Bureau also is experimenting with getting information from administrative records kept by government agencies such as Social Security and the Internal Revenue Service, in cases when people don’t respond.

“The world has changed, and we’re changing our methodology with it,” said Lisa Blumerman, assistant director for the dicennial census program.

The 2010 Census was done in a decidedly old-fashioned way. People got postcards and paper forms in the mail and sent them back. Since then, the Census Bureau has experimented with an Internet option for the American Community Survey, an ongoing random sampling of households that provides figures on income, mobility and a host of other topics that help gauge how Americans live today. About half have replied online.

Forms sent to a D.C. resident. (U.S. Dept of Commerce)

When applied on a national scale, greater use of the Internet to answer census questions would mean the Census Bureau would have to open fewer field offices and hire fewer temporary workers to conduct follow-up home visits to people who didn’t respond.

The Census Bureau estimates it may need only 150 regional offices and 150,000 field workers for the 2020 count, less than a third of the 500 offices and 550,000 workers needed in 2010. The Census Bureau said it hopes the field workers, though pared in number, will have more time to focus on reaching out to groups that are habitually undercounted such as minorities and the poor.

A series of tests eventually will be conducted in different parts of the country. An initial test was done last year in Philadelphia, but it was much smaller in scope and scale.

Each test has a slightly different focus. The test in which residents of the District and Montgomery County are serving as guinea pigs is designed to assess what kind of approach best motivates people to respond quickly, a task that has been growing difficult for researchers conducting many kinds of surveys.

“We’re looking at optimizing self-response,” said Burton Reist, chief of 2020 Census research and planning.

The District and Montgomery County were chosen as test subjects in part because of their proximity to Census Bureau headquarters in Suitland and in part because researchers were looking for jurisdictions that have densely packed urban neighborhoods near less developed areas, Blumerman said.

The neighborhoods chosen for the test are highly variable. In some cases, researchers zeroed in on specific blocks within larger neighborhoods because they met the criteria for a range of household sizes, a mix of renters and owners, vacancy rates and response rates in the 2010 Census.

The test started early in June and is being conducted in waves into the fall. Some households received a postcard asking how they wish to be contacted for the census, including by e-mail and text message. Some got an e-mail saying they will be contacted again within a few weeks. Others were sent a letter inviting them to go directly online to answer questions.

If previous patterns hold true, about 50,000 households won’t bother to even acknowledge the census entreaty. The Census Bureau expects to learn a lot from them, nevertheless.

In some cases, researchers will look for answers within administrative records already maintained by government agencies — the so-called “big data” sources of a lot of basic information the census is seeking to count precisely.

Other households will receive the traditional follow-up visits. The Census Bureau expects to hire about 1,000 people in the region to do these visits in jobs that generally pay $18.50 to $21.50 an hour.

The test will cost about $12 million, including printing, postage, leasing space and wages for field staff. Census officials say what they will learn will save far more.

“D.C. and Maryland residents who participate now in this test are helping us find ways to reduce taxpayer costs for the 2020 Census,” said Census Bureau Director John H. Thompson in a statement posted to the agency’s Web site. “The Census is mandated by the Constitution and is fundamental to our democracy, and by participating today, D.C. and Maryland residents are contributing to research on the effectiveness and efficiency of new operations, which will inform major design decisions made in late 2015 for the 2020 Census.”