Almost every county in the U.S. has its share of haves and have-nots. But there are some regions where it's just plain harder for Americans to thrive, places where the poor far outnumber those living in middle-class comfort.

Ten counties in America stand out as the most challenging places to live, based on a survey of six criteria including median household income, disability rate and life expectancy, according to an analysis by The New York Times.

The county with the dubious distinction of being the worst of all is Clay County, Kentucky, where residents can expect to die six years earlier than the average American. But it's not a recent distinction for the Appalachian county. Its reputation as a rough area dates as far back as 1899 thanks to clan feuds, while a recent survey found Clay County had the worst health characteristics of any county in the state.

Clay isn't the only Kentucky county to make the list, according to the Times. A cluster of Appalachian counties rank among the toughest places to live in America, with five additional coal-region Kentucky counties on the list: Breathitt, Jackson, Lee, Leslie and Magoffin.

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The other four counties ranked at the bottom of the survey include four counties in the rural south: Humphreys County, Mississippi; East Carroll Parish, Louisiana; Jefferson County, Georgia; and Lee County, Arkansas.

The findings highlight an often overlooked issue in the debate about income inequality -- the stubbornness of rural poverty. In the U.S., the number of poor rural residents outnumber those in the cities, with 14 percent of rural Americans living below the poverty line, compared with 12 percent in urban areas, according to the International Fund for Agricultural Development's Rural Poverty Portal.

Half a century ago, Kentucky provided the face for President Lyndon Johnson's "War on Poverty." But while the U.S. poverty rate has declined to 16 percent, from almost 26 percent in 1967, poor rural counties are now facing new issues, such as obesity and drug addiction, and longstanding problems, such as a lack of employment opportunities.

There are a lot of ideas on how to help struggling regions around the U.S., but no clear answer. One proposal floated by Kentucky Senator Rand Paul is to create "economic freedom zones" in challenged U.S. cities, cutting income taxes to a flat 5 percent in order to attract employers.

But the problems in America's hardest-hit counties go far beyond a tax stimulus, and include one aspect that may simply prove insurmountable, at least in the near term: isolation. With Appalachia's poor regions far from major highways, cities and industry, that makes it more difficult for families to find stable jobs or pursue higher education.

More than one-fourth of children live in poverty in 12 states that stretch from Appalachia to Arizona, according to the Population Reference Bureau. Poverty rates are not only higher for rural children than for those in cities, but the growing income gap is also hitting rural families harder, the PRB said in a 2009 report.

Already challenged by its isolated geography and poverty, Appalachia was especially adversely affected by the recession. Median household income in the region between 1999 and 2005 through 2009 declined 7 percent, compared with a decline of 5 percent nationwide.

Of course, Appalachia and the South aren't the only parts of the country where people struggle, The Times' study found. Pockets of economic and social hardship extend from Maine to Alaska.

So where's the best place to live? According to the number crunching, it's Los Alamos, New Mexico, home to the Los Alamos National Laboratory. Thanks to the lab's $2.1 billion budget, the county of about 18,000 residents is prospering.

Other high-ranking counties include several that serve as suburbs to Washington, D.C., and New York City-area counties, such as Westchester, New York (ranked 98th out of all U.S. counties) and Morris County, New Jersey (ranked 43rd).