There's no government agency that requires business owners register their self-employment. You do, however, have to meet all the registration requirements any business does in your city, county or state. These can include applying for a local business license, an employer identification number and registering a business name. Local governments handle a lot of this, and not all of them allow you to register online.
Local Business License
In most parts of the country, you have to take out a business license, even if you're a one-person sole proprietorship. Go to your city or county website -- usually the finance department or the tax collector pages -- and find out how to apply. Even if the application is available online, some local governments require you mail in a hard copy or drop it off at the office.
Registering a Name
If you do business under your own name, you don't have to register it. If you want to be "Wilson's Plumbing and Supply" or "Golden Plumbers," you need to register that you're "doing business as" that name in most states. Usually you register the name with your county clerk. Like your business license, it's up to the county whether you get to register online.
Getting an EIN
A sole proprietor, doing business under your own name, with no employees, probably doesn't need an employee identification number. If you have a different business structure or you hire employees, you apply with the IRS to get an EIN. This identifies your business on tax returns the way your Social Security number identifies you. The IRS prefers you apply online (see Resources).