From time to time a news outlet or publication will come up with a list of the wealthiest US cities, states or counties. Such lists can be misleading for many reasons. First, there are obviously very different areas in states or counties, and within cities wealth disparities even between neighborhoods on either side of a street or avenue can be very significant. Additionally, most of these lists do not actually count wealth, but income, two very different things. This is, of course necessary because the best data points for such things are tax filings and Census information. However, pure income does miss some very important components of wealth, including investments and property. Finally, these lists do not factor in the critical cost of living disparities between different parts of the country. For example, while someone in a city might make over $100,000 a year, they are also paying more for everything from apples to apartments.
On the other end of the spectrum are the poorest areas in the Union. Some of the same problems that plague the rich lists can also create problems for poor lists. Not everyone in even the poorest counties is 'poor' and wide gaps can exist between citizens of any area. Additionally, as many of the counties on the poor list are rural, it is possible that the wealth of many citizens of such counties is tied up in property, whether it be a farm or the actual land they live on. Presumably the cost of living in such areas is lower as well. Because of these factors it is therefore difficult to know whether 'income' is a true reflection of, for example, standard of living in both the 'rich' and the 'poor' areas.
However, due to a lack of reliable information on all of the factors that would eliminate the problems noted above, focusing on income is usually the best one can do when comparing the wealth of different areas. Additionally, averaging out over entire counties alleviates at least some of the concerns above. Also, even with flaws, such lists are important if for no other reason than their ability to act as a stimulant for otherwise difficult conversations regarding both socialogic and economic phenomena. Finally, Blawgconomics loves lists. Therefore, despite obvious faults, here is a very recent list produced by Newsweek which notes the wealthiest counties in the US along with notes on each. Not surprisingly most all the counties listed have ties to either Washington, DC or New York City. On the other end of the spectrum, such a recent example was not available. However, Wikipedia provides lists of both per capita and household income in poor counties derived in part from Census data.