Cook will start as soon as he resigns from his position in Gilbert and government administrator Bill Wiley steps down as interim assessor. He'll stay in office the length of Petersen's original term, which ends December 31.
Cook told Phoenix New Times he's committed to running for re-election to stay in office beyond this year.
resigned in January after state grand juries in Arizona, Utah, and Arkansas indicted him last October on dozens of felonies in an adoption scheme he allegedly operated out of his private-sector Mesa law firm. He faces charges for his role in arranging for more than 70 pregnant Marshallese women to travel to the United States to give birth, a likely violation of international agreements.
Petersen has pleaded not guilty to all charges but resigned to focus on "defending the allegations against me," he said in January.
Cook, a Republican, has served on Gilbert Town Council since 2011. He's also the president of the Arizona Municipal Water Users Association, and serves on numerous local boards, according to his LinkedIn.
Before entering the political sector, he worked in "corporate America," he says, as a technical account manager for the cloud data services and data management company NetApp.
In politics, Cook said, he's proud that he's been able to transform "local government to run like a billion-dollar corporation" — and he plans to do the same as county assessor.
"It's just been a joy to take local government and transform it into a high-performance, excellent service organization," he said.
The councilman also told New Times it will be his goal to "bring a very highly professional image back to the county assessor's office" after the scandal that erupted over the last several months.
Cook was one of five candidates interviewed for the assessor job, alongside lawyer Thomas Galvin Jr., lawyer Rodney Glassman, former state Representative Laurin Hendrix, and Arizona Department of Revenue Manager Darren Rasmussen, according to a previous board announcement.
At Friday's special meeting, county supervisors mentioned Cook's engineering background and his "one-team" leadership style as reasons his application stood out.
Cook also gave remarks at the meeting after his appointment.
"My mother-in-law who passed a number of years ago had a great thing," Cook said. "She said that [for] every teapot, there is somewhere a lid. You have found a new lid for this teapot."