This map from The Daily Yonder, shows the percentage social security payments represent in county income totals. These have a heavily rural orientation to them. A number of factors account for this.
1. Farming areas have been becoming older, therefore in social security's basic service range, for some time. Younger farms have troubles starting or replacing older farmers. The startup costs are very high.
2. The urban place attracts young people and so the percentage would decline. Note the more poverty prone areas in the country have higher percentages. Go down the Appalachians and onto rural Missouri. Note the reservation areas included, particularly in the West.
3. Many retirees move to rural areas for a calmer, more secure life. These can involve lakeside homes as well as small town living.
Of interest is the Von Thunen circular areas. Look at the pattern radiating out from the Chicago-Milwaukee-Detroit core. Upper Michigan and Wisconsin have the higher percentages. The same is there for the Boston-Washington core, but less clearly marked by zones. You have another zone of this around Dallas-Fort Worth.
Von Thunen rings: Study Blue. http://www.studyblue.com/notes/note/n/chapter-1-keyterms/deck/6052238
Sociual Security map: The Daily Yonder. http://www.dailyyonder.com/rural-counties-most-dependent-social-security/2011/11/02/3584