Half the Country Lives in These Counties - This map used Census data to determine that half the people in the United States live in these 146 shaded counties. You can see a list of those counties on the original Business Insider post.
Poverty in the US, a recent mapping of this feature. Citation: Holt, James B. The topography of poverty in the United States: a spatial analysis using county-level data from the Community Health Status Indicators project. Prev Chronic Dis 2007;4(4). Source on the web: http://www.cdc.gov/pcd/issues/2007/oct/07_0091.htm