Is That Business Name Already In Use?

For businesses in your local area, check with the county clerk's office. Many counties now have their assumed name database online. Those that don't will require a visit in person.

Registering your name as a trademark is also a good idea. It's not required by law, but trademark registration can protect you if another business later tries to use your business name, or one that is similar.

If you plan to market your service or product in more than one state, you should file an application for federal trademark protection by registering your business name with the U.S. Patent and Trademark Office.

There isn't a one-stop place to find out whether a business name is already in use, so it requires some checking around.Firsts of all to watch out,Is the business in the same industry as yours? Is it operating nationally or solely in its local area? Would prospective customers confuse your business with the other business?
Under federal trademark law, a business can claim rights to a name if it's first to use a name in a particular category of business in the geographic area it serves.
A business still has rights to the name if it is using the name publicly -- even if it hasn't officially registered it for trademark protection.
You can go to the U.S. Patent and Trademark Office's Web site,to see whether another business has officially registered the name for federal trademark protection??
If another business has registered the name, you're typically restricted from using it only if that business is registered in the same category of business as yours or sells the same goods and services. If the businesses are totally different -- say, you're a bakery and the other business using your chosen name is a florist -- then it probably isn't a problem.

Various states (US) have made corporation information accessible online. I know Washington State has done this, haven't looked at others (yet).

Look around YourStateName.gov for relevant info links.