The number of foreigners (i.e. foreign-born people) relative to total population varies across countries. Some countries such as those in Eastern Europe have low foreign-born population since they have been closed economies until the iron curtain fell. Luxembourg(LUX) and Switzerland (CHE) have the highest foreign-born population since they are tax havens. Mexico (MEX) and Poland(POL) have the lowest foreign-born population according to the latest OECD data. In the US, the rate is under 15%.
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Source: OECD Factbook 2015-2016