When asked about their ancestry, about 1% of Americans tell the US Census they are “Scotch-Irish” (also sometimes spelled “Scots-Irish”). Scotch-Irish people trace their ancestry to Protestant Christian Scottish people who moved to Northern Ireland in the 17th century and then immigrated to the US in the 18th or 19th century. The places where a large share of people consider themselves “Scotch-Irish”—which mostly lie in the western parts of North Carolina, Pennsylvania, Tennessee—tend to be Trump country.
A analysis comparing the ancestry of the people in a county and the share of the vote that went to Joe Biden and Donald Trump, shows that Scotch-Irish is one of ancestries most correlated with support for Trump. Other ancestries highly correlated with Trump support include western European ancestries like English, Scottish, Irish, and French. All of these were among the first groups of people to be considered “white” in the US.
Places with people who do not identify a foreign ancestry, but simply say they are “American,” are also unusually likely to go for Trump. In contrast, places with large shares of people who have Chinese, Indian, Filipino, or Russian ancestry tended to go for Biden. (People are allowed to report multiple ancestries.)
Remember that these correlations do not necessarily mean that people with these ancestries are more likely to vote for Biden or Trump, just that places with a lot of those people swung in that direction. The table below shows the correlation coefficient between Biden’s support and the share of people in a county reporting certain ancestries—only those reported by at least 2 million people are included. Correlation is calculated on a -1 to 1 scare. A correlation of 1 is perfectly correlated with Biden, a correlation of 0 means no relationship, and -1 means perfectly correlated with Trump support.
In total, the US Census reports data on over 150 ancestries. The interactive chart below allows you to explore how Biden’s vote share correlates with each of them (you can also see the correlation with people working in different occupations and industries). The Census’s data are based on a survey of 5% of the US population. Therefore, the ancestry and occupation data are not exact. For these data, only counties with at least 50,000 people are included to ensure accuracy. For these reasons, pay more attention to the trend of all of the counties, rather than any one specifically.