Bureau officials are hoping the Internet will encourage more people to fill out the forms, as participation has been a problem in years past.
Mail response rates have declined from 70 percent in 1980 and 65 percent in 1990. Officials estimate that rate will dip to 61 percent this year. The data is critical for the reapportionment of congressional seats and distribution of federal funds.
"The purpose is to make it as easy as possible for people to respond," said Tim Olson, assistant regional census manager in Seattle.
Those who have received questionnaires in the mail can fill out the forms at the bureau's Web site. To access the system, respondents must first type the bar code identification number printed on the questionnaire. The bar code lets census counters know where the questionnaire is coming from.
Two years ago, the bureau scrapped plans to collect census data online because of privacy concerns. When people respond to census questions, the law guarantees that their personal answers about race and income, for example, will be sealed for 72 years.
But those concerns have been allayed, as bureau officials are confident the information cannot be accessed by outsiders.
Nonetheless, if Americans are worried about filling out the forms online, there is always the option of sending them through the U.S. Postal Service, Olson said.