» more from Slideshows

10. Borden County / Mitchell County, Texas

Wealth gap: 103.35%
Borden avg. annual income: $93,417
Mitchell avg. annual income: $45,939

In northwestern Texas, two rural and sparsely populated counties are also quite different when it comes to annual income, with Borden County more than doubling the average household incomes in neighboring Mitchell County. With a population of less than 650 people as of 2010, Borden has had a fortunate economic history: It was home to the inventor of condensed milk, Gail Borden Jr., after whom the county is named. Then in 1949, oil was discovered there, yielding several hundred million barrels and supplementing the incomes of the area’s farmers and ranchers. The county has seen its population decline since the 1950s, while the average annual household income in Borden now stands at $93,417.

To the southeast, Mitchell County has a considerably larger population, but residents have much lower annual incomes, averaging $45,939. Mitchell’s median income is $37,260, according to the Census Bureau, while Borden’s stands at $58,409, suggesting a greater income disparity within Borden than compared to Mitchell.

Photo: CNBC.com