The former Massachusetts governor's appearance at the Renée and Henry Segerstrom Concert Hall was his fourth Orange County stop since March. Tickets to the event started at $1,000 and reached $50,000.
Among the attendees were Costa Mesa councilmen Jim Righeimer and Steve Mensinger.
Romney, who arrived at Los Angeles International Airport on Monday morning, is on a Southland tour. He spoke in L.A. before coming to Orange County.
Across the street from the concert hall within the Segerstrom Center for the Arts, protesters waved mostly pink signs supporting Planned Parenthood. Protesters chanted "Mitt Romney's got to go."
Whittier resident Marissa Moritz, 29, said Romney's stances on women's rights are disrespectful and would take women backward.
Women's rights, though, aren't her only issue with Romney. She held a sign asking for Romney to release his tax returns.
"I don't feel that Romney understands the average American and the struggle we're going through right now," she said.
Local comedian Dina Marion waved red, white and blue pom poms and chanted in front of the concert hall in support of Romney.
As a Libertarian, Marion said she supports Romney because he believes in God and he can get the country back on track.
"Our country is going down fast, and this is a last-ditch effort to save us," she said.
Romney last visited Costa Mesa on July 23, when he met with business owners and executives at the Endural LLC plastic container plant on Scenic Avenue. He also made a fundraising stop at the Balboa Bay Club and Resort in Newport Beach on June 1.