Most counties dependent on exports are small, so they could be hurt most by changes to NAFTA

Changes to the North American Free Trade Agreement could have an outsized impact on many places in rural America. "Although counties containing big cities such as Los Angeles, New York and Houston generate the highest dollar volumes of exports, the most export-dependent places tend to be relatively small, often rural or suburban counties whose economies are based on a single industry – or sometimes even a single company or plant," Drew DeSilver reports for the Pew Research Center. "In fact, of the 154 counties or county equivalents where exports accounted for more than a quarter of GDP last year, only 11 had populations above 100,000 and half had fewer than 25,000 residents, according to a Pew Research Center analysis of data compiled by the Brookings Institution for its 'Export Monitor 2017' report." Many of the high-export counties manufacture automobiles or auto parts.

Pew Research map; click on it to enlarge it.

Three U.S. counties rely on exports for more than 50 percent of the local gross domestic product. Leading the pack is Hancock County, Ky., a county of 8,810 residents which brings in 55.3 percent of its GDP from manufacturing aluminum and other nonferrous metal products.

In the counties with the greatest growth in exports, "booming U.S. oil and gas production and higher precious-metals prices have turbocharged export growth in many resource-rich counties. In 17 of the 30 counties with the highest annualized real export growth rates between 2003 and 2016, the economic sector that contributed the most to that growth was mining, oil and gas extraction," DeSilver reports.

Canada and Mexico are the two biggest destinations for U.S. exports, so a change in the U.S.'s trade relationships with those countries could hurt rural America. The NAFTA renegotiation talks are ongoing, but have been granted an extension after negotiators have had a hard time meeting stringent American demands.