ORIGINAL POST, 12:01 pm:

Multnomah County Chairman Jeff Cogen is resigning, effective Sept. 16.

"I've always told my children that we must face the consequences of our actions," Cogen writes in a statement. "It is time for me to follow my own advice."

Cogen's chief of staff, Marissa Madrigal—who resigned from working for him Thursday—will take over as County Chair on Sept. 17, and serve through the May 2014 election.

In July, Cogen confessed to a two-year affair with county employee Sonia Manhas. Documents released by the county showed he used his power and public money to conduct the affair.

He is currently under criminal investigation by the state Department of Justice.

In his resignation statement, Cogen says he expects to be cleared—but wants to spend his time making amends to his family.

"Over the past several weeks, I have been reflecting both on the mistakes I have made, and on the best interests of Multnomah County government and the people that it serves," he writes. "People want to move on from this distraction. They deserve to."

Cogen's decision to step down comes after more than two months of defiance—including casting the only vote against a symbolic demand for his resignation by his four Multnomah County board colleagues July 25.

UPDATE, 12:25 pm: Portland Mayor Charlie Hales says Cogen is right to resign.

"I wish him well," Hales says. "I wish his family well. He did the right thing. The city and the county have a lot of work ahead of us. Jeff's decision today clears the way for our common constituents."

UPDATE, 12:30 pm: Multnomah County officials attending the today's Portland City Club debate are learning of Cogen's resignation on their mobile devices.

UPDATE, 1:23 pm: County Commissioner Judy Shiprack says she's pleased Cogen resigned.

"I think it's a good thing," she says. "It's been difficult to work around the circumstances he brought on the county."

Shiprack says her first priority is getting a permanent county chair for the next budget cycle. She's leaving the City Club debate to head back to county offices to see if Cogen has resigned in time to call for a special election.

UPDATE, 1:35 pm: Marissa Madrigal, who will take over as County Chair on Sept. 16, says she's committed to serving as long as needed.

"Things are happening very quickly," Madrigal says. "I'm laser-focused on how to make sure this transition is smooth and [be] a good caretaker of the county."

Madrigal says she knew when Cogen designated her his successor that she could assume the county's top job on short notice. But she says the last 24 hours—she resigned as Cogen's chief of staff, only to have him essentially give her his job shortly after—were like nothing she imagined.

"It's been a roller coaster," Madrigal says. 

UPDATE, 2:30 pm: Oregon Department of Justice spokesman Jeff Manning says the state's criminal investigation of Cogen is not affected by his quitting.

"The resignation does not change anything as far as we're concerned," Manning says. "We'll just keep on plugging away."

Manning adds that Cogen gave Attorney General Ellen Rosenblum's office no warning he was about to resign. "Neither he nor his people gave us any heads up," Manning says.

UPDATE, 2:45 pm: Multnomah County Commissioner Deborah Kafouryalready the most powerful figure in county politics and the frontrunner for chair—says she's not ready to announce her candidacy for Cogen's job.

"I'm not going to make any announcement today," Kafoury says. "It's not the right time. I will announce something soon."

Kafoury echoes the relief voiced by other regional officials.

"The employees of Multnomah County... have been through a lot in the last two months," she says. "Everyone will be happy to get back on the right track and return to some stability."

UPDATE, 5 pm: Here's one reason for the timing of Cogen's resignation: By quitting after the Sept. 5 filing deadline for a November special election, he guarantees that no election can be held for his office until May 2014.

"If [the resignation] had been earlier this summer," says Eric Sample, spokesman for Multnomah County Elections, "the board could have called an election."

By waiting until today, Cogen—who rebuffed his colleagues' calls for him to resign in July—maintains some power over the future of the chair's office, by controlling the timeline.

In particular, he blocks Commissioner Deborah Kafoury, one of four colleagues who issued the July resolution calling for his resignation, from quickly taking his office in a November election.