The addition of those counties means that more than half of all U.S. counties - 1,584 in 32 states - have been designated primary disaster areas this growing season. The majority of them are in a drought that is considered the worst in decades.
The announcement included counties in Arkansas, Georgia, Iowa, Illinois, Indiana, Kansas, Mississippi, Nebraska, Oklahoma, South Dakota, Tennessee and Wyoming.
The USDA uses the weekly U.S. Drought Monitor to help decide which counties to deem disaster areas, which makes farmers and ranchers eligible for federal aid, including low-interest emergency loans.
To help ease the burden on the nation's farms, Agriculture Secretary Tom Vilsack unveiled new help for frustrated, cash-strapped farmers and ranchers grappling with extreme dryness and heat. Vilsack opened up 3.8 million acres of conservation land for ranchers to use for haying and grazing. Under that conservation program, farmers have been paid to take land out of production to ward against erosion and create wildlife habitat.
Along with federal aid, Vilsack said crop insurers have agreed to provide farmers facing cash-flow issues a penalty-free, 30-day grace period on premiums in 2012.
The USDA's National Agricultural Statistics Service determined that as of this week nearly half of the nation's corn crop was rated poor to very poor. About 37 percent of soybeans were lumped into that category, while nearly 3/4 of U.S. cattle acreage is in drought-affected areas, the survey showed.
The Associated Press contributed to this report.