The Crank star exchanged vows with Oosterhouse on Saturday in his hometown of Traverse City, Michigan.
The couple, both 35, confirmed its engagement in April.
Smart was previously engaged to actor Branden Williams.
An insider says the proposal happened four days ago and took place in L.A. "It was a very big surprise but she is thrilled and very excited," a snitch source says. "They are perfect for each other."
Smart, 31, and Oosterhouse, 34, met in November 2010 at a green-charity event. "He's an eco-carpenter; Amy drives a hybrid and is the greenest girl I know," a source gushes. "They are perfect for each other." Oosterhouse is well-known for his work as carpenter on TLC's "Trading Spaces" and his hosting gigs on Hgtv's "Carter Can" and "Red Hot & Green."
A source says, "Here are two wholesome, kind, sweet Midwestern types. Neither has sold out and gone Hollywood." Smart ended her 15-year relationship with Branden Williams last year.
"They have lots of common interests," a source told People. "It's still pretty new, but they seem to be having a blast together." Oosterhouse fronts America's home improvement show "Carter Can".
Smart previously dated actor Branden Williams for more than a decade, according to People. In April 2009, Smart told Playboy she and Williams were living together but had been dating on and off for 15 years. It's unclear why they split.
She said back in 2004, "Relationships are the hardest thing in the whole world. The only downside in this business is temptation - all the pretty people, the glamor, the parties, the opportunities."
The actress, 34, and her beau were spotted "stealing kisses" at an Art of Elysium event in Los Angeles on Saturday.
Smart previously dated actor Branden Williams for more than a decade, according to People.com. Oosterhouse fronts America's home improvement show Carter Can.
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