Using this site, you can enter a street address and retrieve information for the census tract in which the site is located. Median family income, population, number of housing units, and ethnicity for the tract are examples of data available.
REDI works to attract businesses to Columbia & Boone County. They provide demographic data (look under "Programs" & then "Attract") as well as data on quality of life, buildings and sites, and the business environment.
This is a good place to start when looking for any type of data including demographic. The focus is U.S., but there is some information on foreign countries as well. Remember, the numbers in the index refer to table numbers, not pages. For international data, look under foreign countries in the index.