If you are looking to use US Census data, the American FactFinder website: https://factfinder.census.gov/faces/nav/jsf/pages/index.xhtml allows you to search for Census data in different ways and then download tables in csv format.
For example, on the Community Facts site, you can enter a state, county, city, town, or zip code and obtain the population of the geography that you entered. Then you can click on the subjects listed on the left side of the page (Age, Business and Industry, Education, etc.) to see other interesting information about your geography, or click the links under "Popular tables for this Geography" to see tables containing other data for your community.
Or you can use the Advanced Search feature to search all available data using all of the search features provided by the site.
Also, I don't know much about this myself, but there exists at least this one Github repository with "SQL scripts and other supporting files for importing recent American Community Survey releases from the US Census Bureau datasets". The scripts are released under the GNU General Public License.