In Nevada, Brian Sandoval made history as he became the state's first Hispanic governor, CNN reported.
Jerry Brown, who was chief executive in California from 1975 to 1983, moves into the governor's mansion again at age 72.
Former U.S. Sen. Mark Dayton takes over for outgoing Minnesota Gov. Tim Pawlenty, considered by some to be readying a bid to be the Republican presidential candidate in 2012.
In Wisconsin, GOP Tea Party movement favorite Scott Walker takes over from Democratic Gov. Jim Doyle, who retired.
Republican attorney and rancher Matt Mead succeeds Democratic Wyoming Gov. Dave Freudenthal, who was barred from a third term by term limits.
"An exciting new chapter starts as I will be sworn in," Brown wrote on his Twitter page. "Here's wishing you exciting new chapters in this new year!"
In his final weekly address, Gov. Arnold Schwarzenegger thanked Californians "for allowing me the honor of serving as your governor."
"I came to California four decades ago with absolutely nothing. Because of this state welcoming me with open arms, I gained absolutely everything," he said.
Dayton's victory allows Democrats to hold onto a 20th statehouse, compared with the GOP sitting in 29 governor's chairs, though he will have to contend with a GOP-controlled Legislature. Rhode Island's governor, Lincoln Chafee, who will be sworn in Tuesday, is independent.
Several other governors have taken office in recent days, CNN said. On Saturday, Democrat Andrew Cuomo took the oath to be New York's governor, while Republican Susan Martinez was sworn in in New Mexico, becoming the first female Hispanic governor in the United States.
Former healthcare executive Rick Scott, a Republican, will replace Florida Gov. Charlie Crist Tuesday.
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