Median household income: $91,104
Just a hop, skip and a subway ride from Manhattan, Nassau County contains a large chunk of Long Island and Long Beach.
The only New York county to make the list, this area has an extremely low poverty rate, with only 5% of residents living below the poverty line. But what really sets Nassau apart is its diversity, with 20.7% of foreign-born residents and 27.3% of its residents speaking a language other than English at home. 10th richest: Morris County, N.J.
Median household income: $91,469
Morris just barely snuck into the top 10 richest counties after its median household income fell by roughly $3,000 from 2009. The county's residents are less than an hour from Manhattan, and the area includes several lakes and state parks. Golfing is big in Morris county, with about 20 places to tee off.
Median household income: $92,655
Not to be outdone, Virginia matches Maryland with the most counties on our list. Prince William has seen its median household income increase from 2009, even as the national average declined.
Prince William is outside of Washington, D.C., just like several other on the list. What makes it stand out from the rest, though, is the 43.2% population boom it has seen in the past decade. The area is home to many historical sites, including the Manassas National Battlefield Park, where two Civil War battles took place. Eighth richest: Somerset County, N.J.
Median household income: $94,270
With one of the most prestigious colleges in the country just outside the county line (Princeton University), it's no surprise the education levels of Somerset County's residents are very high. Almost 93% of residents have a high school diploma and roughly 50% have a bachelor's degree or higher. Seventh richest: Stafford County, Va.
Median household income: $94,317
With just 128,961 residents, Stafford County is one of the smallest population areas on our list, but what it lacks in size it makes up for in jobs. The county's unemployment rate is just under 5%, much better than the national average of 8.3%.
The wealth of jobs must put residents in the giving mood, since the state of Virginia also came in at the third spot on our list of the most generous states in the U.S. Sixth richest: Douglas County, Colo.
Median household income: $94,909
The only Colorado county and the only county west of the Mississippi to make our list, there's something special about Douglas. The large youth population (30.5% of residents are under the age of 18) suggests that the county is a good place for families.
Lying just outside of Denver, residents only need to travel up Interstate 25 to get to the Mile-High City. The rural beauty must attract residents, as there are only 339.7 people per square mile and the population has seen a 62.4% increase from 2000-10.