Jan Callison, who has played a centrist role on the Hennepin County Board for the last decade, has announced that she will not seek re-election to the board in 2020.

In a Facebook posting and in her monthly e-mail newsletter released Monday, Callison said that she had decided not to run for what would be her fourth term "after considerable reflection."

She called representing the Sixth District "a privilege and a joy," but said that she had decided to end her time in office "after more than two decades of public service at the city and county level."

Callison, of Minnetonka, was first elected to the board in 2008 and was re-elected twice by wide margins, winning with 61% of the vote in 2016.

She became board chairwoman in 2015, only the second woman to hold that position at the time, and served until early this year, when Commissioner Marion Greene was elected to succeed her.

Callison currently chairs the county's Regional Railroad Authority, and also serves on the Hennepin Healthcare System Board.

Callison, a strong proponent of the Southwest light-rail line, also sits on four committees and boards steering the Southwest project.

A Harvard-educated lawyer, Callison was director of an affordable-housing land trust and a regional leader on environmental and planning issues. She served 15 years on the Minnetonka City Council, including three as mayor, before joining the County Board in 2009.

When she took office, she said she had no agenda and called herself a moderate who had won backing from both a former Republican governor, Arne Carlson, and a former DFL secretary of state, Joan Growe. She has run for office without party endorsement.

"I view local government and county government as being practical and pragmatic," she said in 2014, when she was expected to become the board's next chairwoman. "We're here to deliver services in the best way we can."

The Sixth District occupies a swath of the county's well-heeled south-central area, including Eden Prairie, Edina, Excelsior, Hopkins, Minnetonka, Mound, Orono, Shorewood and Wayzata.