Hennepin County Commissioner Mike Opat, the prime architect behind construction of Target Field, won't seek re-election in November after nearly three decades in office.

The 58-year-old DFLer said it's been a "great honor" to serve on the County Board, but that "the time is right for me to move on to new challenges."

Opat, who lives with his family in Robbinsdale, represents the county's First District, which includes the county's northeastern cities of Brooklyn Center, Brooklyn Park, Crystal, New Hope and Osseo as well as Robbinsdale.

"To say I've been proud to represent the District 1 cities would be an understatement," he said in a statement. "This district is home to the extended Opat family, many new Americans and lifelong suburban residents."

Opat is the third of Hennepin County's seven commissioners to announce they are leaving the board at the end of the year. Commissioners Jan Callison and Jeff Johnson have announced they won't seek re-election this fall.

Opat said he didn't have a new job lined up, but added he wants to pursue another career before retiring.

He provided a long list of accomplishments from his 27-year tenure, including the beginnings of the Bottineau light-rail line, expansion of transit, the Humboldt Greenway, the Brookdale Library and governance changes at Hennepin Healthcare.

He said he was proudest of improving services and infrastructure in his district, while "leveraging the size and scale of Hennepin County to deliver projects that benefit residents across the county and the state."

Opat acknowledged that none of what he considers accomplishments could have been achieved without his board colleagues, public workers and business leaders.

He was first elected to the County Board in 1993, ousting longtime Commissioner John Derus in an upset. Opat was elected board chairman in 2001 and re-elected nine times to that position.

He is a native of Minneapolis who worked full time at the Hennepin County workhouse while attending the University of Minnesota. He received a master's degree in public policy from Harvard University's John F. Kennedy School of Government in 1989, and returned to work at the jail before his successful run for the board in 1992.

He led the county's campaign to build Target Field, which may be the most visible representation of his work. But Opat had a firm and often-stated commitment to making the county a safety net for its most vulnerable residents.

When Opat stepped into the debate about how best to build the Twins ballpark, discussions had been going on for years without a solution. Most politicians either disliked the idea of a publicly subsidized ballpark or were unwilling to risk their careers to sponsor it.

Led by Opat, the board approved a countywide sales tax to finance the ballpark. It opened in 2010 and is on track to be paid off a decade earlier than forecast.

Opat and his wife, Kim, have three children.

Rochelle Olson • 612-673-1747 Twitter: @rochelleolson