If you or your child has a school report due tomorrow, the Census Bureau site will not be available to help. Census.gov and its affiliates, like American FactFinder and online surveys, are offline as part of the federal government's shutdown. The same goes for the Federal Trade Commission's site, the Agriculture Department's USDA.gov and the Library of Congress' site, which can also be a rich resource of reference information.
The decision to put up a splash page is an agency-by-agency call. When you visit the Census site today, instead of a portal to troves of data, you'll get this message: "Due to the lapse in government funding, census.gov sites, services, and all online survey collection requests will be unavailable until further notice."
Technically speaking, a site can stay up because servers are paid for ahead of time. And for most of these sites, a human doesn't have to be working with them to allow them to keep running. The Office of Management and Budget's guidance says this:
"The mere benefit of continued access by the public to information about the agency's activities would not warrant the retention of personnel or the obligation of funds to maintain (or update) the agency's website during such a lapse ... . If it becomes necessary to incur obligations to ensure that a website remains available in support of excepted activities, it should be maintained at the lowest possible level. For example, in the IRS case, the IRS website would remain active, but the entire Treasury Department website would not, absent a separate justification or a determination that the two sites cannot not feasibly be operated separately."
Other agencies aren't ending their sites so abruptly. The Department of Health and Human Services, for example, not only kept its site up, it also is working feverishly to keep healthcare.gov running that's the main site to sign up for the new health insurance exchanges.
The Sunlight Foundation, which uses some of the source data from government sites, explains further.