The locational distribution and socio-economic determinants of social media are analyzed for the United States counties in 2012. A theory of determinants is presented that is modified from the Spatially Aware Technology Utilization Model (SATUM). Socio- Economic factors including demography, economy, education, innovation, and social capital are posited to influence social media factors, while spatial analysis is conducted including exploratory analysis of geographic distribution and confirmatory screening for spatial randomness. The determinants are identified through OLS regression analysis. Findings for the nation indicate that the major determinants are demographic factors, service occupations, ethnicities, and urban location. Further subsample analysis is conducted for the U.S. metropolitan, micropolitan, and rural subsamples. The subsamples differ most evidently in effects of ethnicities and construction occupations, and there are inverse effects of social capital at the micropolitan and rural levels. The regression findings are discussed in terms of the literature mostly of larger geographic units, and the few nationwide studies at the county level. The exploratory spatial analysis generally indicates similar national geographic patterns of use. Among the results is that although Twitter users are more heavily concentrated in southern California and have strong presence in the lower Mississippi region, Facebook users are highly concentrated in Colorado, Utah and adjacent Rocky Mountain States. Social media usage is lowest in the Great Plains, lower Midwest, and South with the exceptions of Florida and the major southern cities such as Atlanta. The overall extent of spatial agglomeration is very high and is examined in detail for the nation and subsamples. The paper concludes by discussing the policy implications of the analysis at the county as well as the national levels.