It isn't free, but the following is an option:
The data comes from the Census Bureau American Community Survey. The ACS is free to download, but it is a pretty large data set that can be didfficult to work with.
Old question but I will throw in a secondary source:
On this site you can find, filter and download (+ visualize) aggregated data from multiple years of IMF World Economic Outlook forecasts (most recent here). The data is available on the IMF site, but not aggregated across years (so you have to ...