Drawing from a larger study on restaurant nutrition, this cross-sectional study reports on the sodium density of 30,073 menu items from 237 unique U.S. chain restaurant brands in 2010. Sodium density, defined as mg sodium per 1000 kcal, was evaluated with descriptive statistics and stratified by restaurant characteristics (service model and cuisine), menu type (regular or children’s), and item type. The investigation found that sodium density was very high overall, averaging 2196 mg across all regular menu items, and varied widely by restaurant characteristics and item type. By service model, buffets featured the most sodium-dense foods and upscale restaurants the least. By cuisine, pizza and burger restaurant items were lower in average sodium density than in sandwich, Asian, and chicken restaurants. Sodium density was lower overall for children’s versus regular menu items. The United States Department of Agriculture (USDA) recommended upper limit for sodium is 1500 to 2300 mg/day for adults, depending upon risk category. The study found the vast majority of entrées had a sodium density which would be incompatible with USDA upper daily limits, providing evidence that consumers are unlikely to stay within recommended limits after eating a restaurant meal.