There is wide geographic variation in Social Security Disability Insurance and Supplementary Security Income participation across the United States. Some policymakers and members of the public may assume that interregional administrative inconsistencies are a major reason for the geographic variation. To test this assumption, and to reveal other potential explanations for the variation, we decompose the total variation into components by examining regional differences in disability prevalence and in program participation among persons with disabilities as well as the correlation between those two factors. We further decompose the variation in participation among persons with disabilities into socioeconomic components. Our findings strongly suggest that geographic variation in program participation is mainly an indication of geographic variation in disability prevalence and socioeconomic characteristics and that inconsistency in program administration is not a major reason for the variation.