Mississippi comes in at No. 1, with a rate of more than 30 percent, followed by Alabama, West Virginia, Tennessee and South Carolina.
California appears in 41st place with 23.6 percent of its adult population classified as obese.
And while the nation has long been bracing for a surge in Medicare as the boomers start turning 65, the new report makes clear that fat, not just age, will fuel much of those bills. In every state, the rate of obesity is higher among 55- to 64-year-olds - the oldest boomers - than among today's 65-and-beyond.
That translates into a coming jump of obese Medicare patients that ranges from 5.2 percent in New York to a high of 16.3 percent in Alabama, the report concluded. In Alabama, nearly 39 percent of the oldest boomers are obese.
Health economists once made the harsh financial calculation that the obese would save money by dying sooner, notes Jeff Levi, executive director of the Trust, a nonprofit public health group. But more recent research instead suggests they live nearly as long but are much sicker for longer, requiring such costly interventions as knee replacements and diabetes care and dialysis. Studies show Medicare spends anywhere from $1,400 to $6,000 more annually on health care for an obese senior than for the non-obese.
"There isn't a magic bullet. We don't have a pill for it," said Levi, whose group is pushing for health reform legislation to include community-level programs that help people make healthier choices - like building sidewalks so people can walk their neighborhoods instead of drive, and providing healthier school lunches.
"It's not going to be solved in the doctor's office but in the community, where we change norms," Levi said.
The Centers for Disease Control and Prevention has long said that nearly a third of Americans are obese. The Trust report uses somewhat more conservative CDC surveys for a closer state-by-state look. Among the findings:
-Mississippi had the highest rate of adult obesity, 32.5 percent, for the fifth year in a row.
-Three additional states now have adult obesity rates above 30 percent, including Alabama, 31.2 percent; West Virginia, 31.1 percent; and Tennessee, 30.2 percent.
-Colorado had the lowest rate of obese adults, at 18.9 percent, followed by Massachusetts, 21.2 percent; and Connecticut, 21.3 percent.
-Mississippi also had the highest rate of overweight and obese children, at 44.4 percent. It's followed by Arkansas, 37.5 percent; and Georgia, 37.3 percent.
-Following Alabama, Michigan ranks No. 2 with the most obese 55- to 64-year-olds, 36 percent. Colorado has the lowest rate, 21.8 percent.
The Associated Press contributed to this story.