Los Angeles had the largest county GDP in 2018. Photo: Apu Gomes/AFP via Getty Images

32.3% of U.S. gross domestic product was concentrated in just 31 counties in 2018, according to government data reviewed by Bloomberg.

Why it matters: All 31 counties included or were near major U.S. cities, signaling that the economy is concentrating in urban areas as economic output from more rural counties is dwindling.

By the numbers: The 31 counties accounted for 26.1% of employed Americans in the country and only 21.9% of the total U.S. population last year. The counties' combined share of GDP continued to rise last year even though their share of the overall population fell.

  • Los Angeles County, which has a GDP equivalent to Saudi Arabia, had the largest county GDP in 2018, adding $395.2 billion to total U.S. GDP from 2001 to 2018.
  • New York City's five counties generated 4.8% of U.S. GDP in 2018, and New York County, home to Manhattan, added $340 billion to total U.S. GDP from 2001 to 2018.

The big picture: U.S. industries are also becoming increasingly concentrated in a few counties. Nearly three-fifths of the information sector's output came from just a few dozen counties — many of which were on or near the West Coast and home to tech giants like Apple, Google and Amazon.

  • The New York City region dominated in national finance, and Los Angeles held the top spot in the arts and entertainment industry.
  • Meanwhile, the agriculture, forestry, fishing and hunting sectors continued to decentralize.

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