That event is being held at the Chateau Carolands, a mansion nestled in the hills of San Mateo County. Ticket prices range from $2,500 for the general reception to $50,000 for a "founder's dinner."
Attendees will include former Gov. Pete Wilson and former Secretary of State George Shultz, according to an invitation for the event.
This afternoon, Ann Romney will attend a "Bay Area Ladies' Luncheon" at the Palo Alto home of Cisco CEO John Chambers and his wife, Elaine.
Local Democrats and a former Department of Commerce official plan to hold a 5:30 p.m. news conference outside of Romney's Hillsborough fundraiser. They say they plan to speak about the former Massachusetts governor's business philosophy and what a Romney presidency would mean for the middle class.
Speakers will include Ro Khanna, former deputy assistant secretary at the Commerce Department; Santa Clara County Democratic Party Chair Steve Preminger; and Ellouise Patton of United Food and Commercial Workers Local 5.
Romney's visit comes on the heels of a Bay Area stopover by President Barack Obama, who came to town last week for several campaign fundraisers on the Peninsula and in San Jose. Tickets to the Obama events reached $35,800.
