More than half of the U.S. population now lives in localities served by accountable care organizations and almost 30 percent live in areas served by two or more, according to new analysis from Oliver Wyman.

The total number of patients in organizations with ACO arrangements with at least one payer—both Medicare and non-Medicare—is now between 37 and 43 million, or roughly 14 percent of the population. That's up from the consulting firm's previous tally last fall, which was between 25 million and 31 million, about 10 percent of the population.

"For many people receiving care from one of these mixed-model ACOs, the shift to full participation in value-based care will be gradual and subtle as the contracts between the ACO and their insurance company migrate to ACO-style contracts," says Rick Weil, a partner in Oliver Wyman's health and life sciences practice group. "Over time, patients should notice that care gets more convenient, more proactive and more effective."