How many federal employees would be affected by a government shutdown?

 More than 800,000 out of some 2.1 million federal workers (excluding the Postal Service) will get sent home if the government shuts down.

Can you give me an agency-by-agency breakdown of the impacts?

Yes. We've been compiling a detailed list here at the Post, but here's a brief overview, showing how many employees are furloughed, and examples of who stays and who goes:

Department of Commerce: 87 percent of the agency's 46,420 employees would be sent home. (The Weather Service remains, Census Bureau employees go home.)

Department of Defense: 50 percent of the 800,000 civilian employees would be sent home while all 1.4 million active-duty military members would stay on. (Environmental engineers, for instance, get furloughed.)

Department of Energy: 69 percent of the agency's 13,814 employees would be sent home. (Those in charge of nuclear materials and power grids stay. Those conducting energy research go home.)

Environmental Protection Agency: 94 percent of the 16,205 employees will be sent home. (Those protecting toxic Superfund sites stay. Most regulators get sent home.)

Federal Reserve: Everyone would stay, since the central bank has an independent source of funding.

Department of Health and Human Services: 52 percent of 78,198 employees would be sent home. (Many food regulators will stay, those overseeing mental health programs would go home.)

Department of Homeland Security: 14 percent of the 231,117 employees would go home. (Border Patrol would stay. Operations of E-Verify would cease.)

Department of Housing and Urban Development: 95 percent of the 8,709 employees would go home. (Those in charge of guaranteeing mortgages at Ginnie Mae would stay, as would those in charge of homelessness programs. Everything else would stop.)

Department of Labor: 82 percent of the 16,304 employees would be sent home. (Mine safety inspectors will stay, those working on economic data in the Bureau of Labor Statistics will get furloughed.)

NASA: 97 percent of the 18,134 employees would be sent home. (Employees working on the International Space Station will stay. Most engineers will go home.)

Department of Interior: 81 percent of the 72,562 employees would be sent home. (Wildlife law enforcement officers would stay, but the parks themselves would close.)

Department of Justice: 15 percent of the 114,486 employees would go home. (FBI agents, drug enforcement agents, and federal prison employees would stay. Some attorneys would go home.)

U.S. Postal Service: Everyone would stay, since the Postal Service is self-funded.

Social Security Administration: 29 percent of the 62,343 employees would be sent home. (Claims representatives would stay, actuaries would go home.)

Department of Treasury: 80 percent of the 112,461 employees will be sent home. (Those sending out Social Security checks would stay, IRS employees overseeing audits would go home.)

Department of Transportation: 33 percent of the 55,468 employees will get sent home. (Air traffic controllers will stay, airport inspections will cease.)

Department of Veterans Affairs: 4 percent of the 332,025 employees would go home. (Hospital workers would stay, some workers in charge of processing benefits would go home.)

A much, much more detailed list can be found in the agency contingency plans prepared here.