Where to find free U.S. demographics information to assist in market research?

I am trying to find U.S. demographics information to better quantify my addressable and target markets. I am interested in learning answers to questions like:
1. How many individuals graduated with a certain degree?
2. How many individuals participate in a particular profession?
3. How many small businesses are currently operating?
4. How many small businesses exist in a particular segment (e.g. restaurant, cafe)?

I would like to know what (free) resources are available over the web to address these types of questions? Even pointing me in the right direction would be helpful. At this point, I believe my biggest issue is I am unsure of where to begin.

There are a couple of good and free sites that will give you some good data. They are:

• US Census: http://factfinder.census.gov/. They have a wealth of information about all sorts of stuff.
• Zap Data: http://www.zapdata.com/. You have to sign up but they do offer a free service
• North American Industry Classification System: http://www.naics.com/. This replaced the old SIC codes. It has a lot of data on small businesses.
• Marketing Sherpa: http://www.marketingsherpa.com/. Should have some free data or at least where to go find some.

Infochimps has a ton of data from various sources, almost all free to download.

Includes all US Census data among others. Searchable.

If you're interested in technology related market research, you might want to look at:

• Forrester
• Gartner
• eMarketer

Your questions are very specific, and would be hard to get solid numbers on.

For example, here is an article regarding engineering/science graduates:
http://news.medill.northwestern.edu/washington/news.aspx?id=94961 The number of students that graduated with a specific degree doesn't appear to be easily found, as the universities/colleges most likely don't need to report to a higher authority when they give out degrees, but you can find articles, again check professional societies, that will aggregate degrees by type to give some numbers.

To get the number practicing a certain profession will be difficult, but to get a rough idea you could check with the professional societies that deal with that profession and they may have an idea, as people will often work outside of their degree, unless they are required to have a license, then you could ask the state about numbers that are licensed (still just an estimate).

For the number of small businesses, you may check with the SBA, but the best bet would be to ask the states, as these should be registered, and they may be able to tell you the number by segment, though I doubt it will be free.

You may need to pay to get this information aggregated already by some marketing businesses, but, I am not into marketing, so I am not certain to whom you would want to ask about that.