Considering median household income at the county level, I did a little research regarding past patterns compared to today. In 1972, the New York Times reported on the wealthiest counties in the United States:

As the article notes, all these counties are suburban counties.

According to Wikipedia, here are the wealthiest counties today:

Almost all of these top 30 are suburban. But the wealthiest counties have shifted toward more counties in the South and West. Some of the same counties are at the top of the list but there are also new counties there as well. What might have happened in 50+ years? Some guesses:

1. Some of the wealthier counties in the 1970 Census matured, now have slower growth, and have more diverse populations. In contrast, the rapidly growing counties today are more in the South and West.
2. Shifts in industry. Manufacturing jobs declined in many places and growing sectors, such as tech and the federal government, generated wealth elsewhere.
3. Measuring at the county level might obscure patterns at the municipality level and at the regional level. For example, this may be less about individual counties and more about a region – say like the Washington, D.C region – growing.

I would be interested to hear how many companies and residents think at the county level these days. If someone were going to move, would they think in terms of Westchester or Nassau Counties outside of New York City like they might have in 1970 or would they think instead of specific communities and suburbs they have heard about?