Not many, actually. Estimates range from about 2.8 million to 9 million (there is no official tally, just estimates). This old news report from WaPo’s Andrew van Dam (data reporter) is a decent summary: Millions of Americans have left the country. Where are they going, and why? | The Spokesman-Review
Of those who live abroad, 1 in 4 do so because of “family reasons” – many of those who move or retire abroad had prior dual citizenship or access to residency/citizenship by “right of descent” rules. Another 1 in 4 are living abroad due to a work assignment.
About 12% of Americans say they considered moving abroad for retirement but probably less than 1% of Americans retire abroad (contrary to the popular media meme of Americans moving elsewhere). Unless you are high skilled and moved when younger to another country and already have a residency visa, or you have an immigration privilege such as marriage to citizen, dual citizenship or a right of descent residency, most Americans (with a few exceptions for some Central and South American countries) cannot retire abroad.
An academic who researches those who move abroad notes that for most people, most moves are “accidental” – that is, a job opportunity, or a love interest with a foreigner.
