Millions of American citizens are currently living abroad. However, the United States does not formally count the number of Americans who move to other countries and does not require its citizens to register an official place of residence. This makes keeping track of American expatriates a challenge.

The United Nations Population Division currently estimates that 2,996,223 Americans are living outside the United States, while the U.S. State Department estimates that there are as many as 9 million U.S. citizens living in over 160 countries. Although there is no clear consensus, most estimates show that the numbers are rising.

Some of the most common reasons that U.S. citizens choose to live in other countries involve career opportunities, research positions, and romantic relationships. Other people move overseas because another country offers cheaper health care or a higher standard of living. (A higher standard of living is often associated with a higher gross national income. Here are the 25 richest countries in the world.)

Many retirees on a fixed income immigrate to countries with a lower cost of living. U.S. citizens may also move for religious purposes or humanitarian causes as well as for adventure, political or cultural concerns, or avoidance of legal matters. In addition, most children born in the United States to foreign citizens are American citizens by birth but may be taken back to their parents’ home country at a young age. These U.S. citizens who only have a tenuous relationship with the United States are sometimes called “accidental Americans.”

To identify the 25 countries home to the most American citizens, 24/7 Wall St. reviewed the United Nations’ International Migrant Stock 2020 published by the Department of Economic and Social Affairs, Population Division. Data in the release was from 1990 only. Countries were ranked based on the number of U.S. citizens living there. All other data is from the UN except for gross national income per capita – a gauge of a country’s wealth. 2020 GNI per capita in current U.S. dollars using the purchasing power parity method came from the World Bank.

Nearly two-thirds of all Americans living abroad reside in just 10 countries. Unsurprisingly, the top two countries are our North American neighbors, Mexico and Canada. In addition, 10 countries in Europe are top destinations, followed by six in Asia, and four in South America.

Five of the countries speak English as the primary language, although English is commonly used in many of these countries for business and diplomacy. Of the top 25 countries that are home to the most Americans, the number of U.S. citizens has increased since 1990 in all but three countries: Greece, Italy, and Puerto Rico. (Here are the years the most Americans have moved since 2000.)

Click here for the countries with the most American expats