The United States ranks as the 10th most developed country in the world, behind nations such as Norway, Australia, and Switzerland, according to the 2016 Human Development Index of the United Nations Development Programme.

The main factors the HDI considers in its analysis are education, income, and life expectancy. While the United States as a whole falls behind a number of Western European and Asia-Pacific countries by these measures, conditions are not uniform nationwide and some parts of the country far outrank most of the nation. In a number of counties, the college attainment rate and median household income are about double the corresponding national figures, and the average life expectancy is higher than in any country in the world.

To determine the best counties to live in, 24/7 Wall St. developed an index based on the three socioeconomic measures used in the HDI — educational attainment, poverty rate, and life expectancy — and ranked counties based on their well-being.

Click here to see the 25 best counties to live in.

Many of the best counties to live in are suburbs of major metropolitan areas, such as Washington D.C, New York City, and San Francisco, where large shares of residents commute to jobs in high-paying industries such as professional, scientific, and technical services and government. In 16 of the 25 best counties to live in, a larger share of workers over the age of 16 commute outside of their home county to jobs — often in large cities nearby — than the national average of 23.9%.

Seven of the 25 best counties to live in are in the Washington-Arlington-Alexandria metro area, where a large share of residents have access to advanced, high-paying jobs in government and defense. Major employers in Falls Church, Arlington County, Fairfax County, and Alexandria include the U.S. Department of Defense, the Department of Homeland Defense, the Department of Commerce, defense contractor Northrop Grumman, and government services company Booz Allen and Hamilton.

Another major cluster of affluent, well-educated, and healthy counties is in the Western Slope region of Colorado. The three counties with the longest life expectancy in the United States — the contiguous Summit, Pitkin, and Eagle — are located in this region, which is known for its numerous tourist and recreation areas and physically active population.

Many of the counties with the highest educational attainment, lowest poverty, and longest life expectancy also lead the nation in employment and population growth. Of the 25 best counties to live in, 22 have lower unemployment rates than the 4.1% national jobless rate. The numerous economic opportunities likely attract new residents to these areas at a faster pace than in most of the country. As a whole, the population of the 25 best counties to live in grew by 7.5% from 2011 to 2016, nearly twice the 3.9% national population growth rate.

While advanced employment opportunities and a healthy job market likely attract new residents to these high income, well-educated, and healthy counties, a number of the best counties to live in rely on tourism and recreation as a main source of their economic activity. Counties such as San Miguel County, Colorado and Teton County, Wyoming are largely comprised of resort towns and may lack the high-paying job opportunities that other affluent areas have year-round. The unemployment rates in both San Miguel County and Teton County is 6.1%, among the highest of any of the best counties to live in and above the national jobless rate.

To identify the best counties in which to live, 24/7 Wall St. created an index composed of three socioeconomic measures — the poverty rate, the percentage of adults who have at least a bachelor’s degree, and life expectancy at birth — and ranked counties based on the index. The selection of these three measures was inspired by the United Nations’ Human Development Index. Poverty, median household income and bachelor attainment rates came from the U.S. Census Bureau’s American Community Survey and are five-year averages from 2012-2016. Population data also came from the ACS. Life expectancies at birth are from the Institute for Health Metrics and Evaluation, a health research center affiliated with the University of Washington, and are for 2014. Unemployment rates are from the Bureau of Labor Statistics and are seasonally adjusted for November 2017. Independent cities in Virginia are treated as counties by the U.S. Census Bureau and are included in this list for that reason.