Mary Brainerd, the HealthPartners chief executive who led significant growth in her 15 years running one of the state's largest nonprofits, announced Monday that she will retire in June.

Brainerd will be succeeded by Andrea Walsh, a longtime executive who has held a variety of leadership positions at HealthPartners, which is both a large health insurance company and a major operator of hospitals and clinics.

The departure is the latest in a series of exits since late 2014 by veteran CEOs at local health insurance companies, in an industry confronting big changes with the federal Affordable Care Act.

"Her tenure has been a very successful one," said Allan Baumgarten, an independent health care analyst in St. Louis Park. "During her time, HealthPartners has, through a series of acquisitions or mergers, established itself as the third largest [health care] provider system in the Twin Cities. It also continues to expand as a health plan company."

Brainerd became CEO in 2002. In 2012, she led a merger with the St. Louis Park-based Park Nicollet system that expanded the health care delivery side. Brainerd also led mergers with hospitals in Stillwater and western Wisconsin.

Today, HealthPartners employs more than 23,000 people. With operations that include Regions Hospital in St. Paul and Methodist Hospital in St. Louis Park, HealthPartners in 2015 posted $5.7 billion in revenue — more than triple the nonprofit's 2002 revenue of $1.8 billion.

"I think there's a much greater balance and diversification within HealthPartners," Brainerd said. "Health care has gotten bigger. We've tried to keep our values at the forefront as we've gotten larger, as well."

Walsh, who grew up in Rochester, has been a member of senior leadership, serving most recently as executive vice president. Before joining HealthPartners, Walsh practiced law and was an assistant commissioner at the Minnesota Department of Health.

HealthPartners is one of a handful of groups across the country that for decades has combined care with coverage — an approach that has been part of the federal government's push for "accountable care organizations."

The idea is that by bringing care and coverage together in one organization, the ACO will have incentives to coordinate care to save money and improve patient care.

"HealthPartners has had a long history with care and coverage together, as the way our founders started the organization," Walsh said. "But our work clearly is not done."

Brainerd, who grew up in St. Paul, started at HealthPartners when it was formed in 1992 with the merger of the old Group Health and MedCenters. At that point, the company provided coverage and clinic care, but had no hospitals.

Now, the health system includes seven hospitals, Brainerd said in an interview, adding that the number of doctors has grown from 250 to 1,800.

Brainerd is one of the founding CEOs and former chair of the Itasca Project, a group of 40 business leaders that work to drive long-term economic growth in the Twin Cities. She also expects to continue working on the board of directors of Minnesota Public Radio, Bremer Bank and Securian Financial Services. She also plans to spend more time with friends and family.

"We've had a very solid financial performance over a very long period of time," Brainerd said. "I … think it's a great foundation for the future."

Twitter: @chrissnowbeck