Here's the map, with said counties shaded in. Below the map is the list of all the counties, so you can see if you live in one of them.
Using Census data, we've figured out that half of the United States population is clustered in just the 146 biggest counties out of over 3000.
Here's the map, with said counties shaded in. Below the map is the list of all the counties, so you can see if you live in one of them.