There is a growing diabetes epidemic in the United States and if we are to halt its progress we need to better understand the social determinants of this disease and its control. Social capital, which has been associated with general health and mortality, may be one important mediator of glucose control. In this study we determine if neighborhood social capital is associated with glucose control, independent of individual factors. We performed a cross-sectional study of Black veterans with diabetes living in Philadelphia. We merged individual-level data from surveys and charts with six area-level social capital descriptors. Holding all other variables constant, patients who lived in neighborhoods that scored near the 5th percentile of working together to improve the neighborhood were estimated to have glycosylated hemoglobin (HbA1c) values that were at least one point above a conservative clinical definition of “diabetes control” (HbA1c ≤ 8%). If these same patients were to live in neighborhoods in the 95th percentile, their expected HbA1c would be over ½ a point below the cut-off value 8%. No other measure of social capital was associated with HbA1c. In this study of black veterans with diabetes we observed that living in neighborhoods where people work together is associated with better glucose control.