I am looking for foreign-born population by county in 1970, 1980 and 1990. I tried to aggregate individual-level data from IPUMS USA to county level, but found that most of the counties don’t have any data. Where can I find tables that documents foreign-born population (or as a percentage of total population) by county in 1970, 1980 and 1990? Thank you!
Since aggregate data is what you seek, the NHGIS project, which is also housed at the Minnesota Population Center, will suit your needs perfectly. NHGIS offers many of the official Census tables going back to 1790 at several geographic levels, including county. While NHGIS is primarily focused on mapping data, the summary tables can be extracted independent of shape files as .csv files with optional descriptive headers.
On the data finder page, choose “county” for the geographic level, “1970 and 1980 and 1990” as the years, and “Nativity and Place of Birth” as the topic. The time series table titled “Persons by Nativity [2]” will provide you with the number of foreign- and native-born individuals by county for each of your years of interest.
Hope this helps!