The "Batman Begins" actress and Foxx, 49, who have always kept their relationship private, flew to the Mexican resort city for a "quick trip", reported Us weekly.
"Katie and Jamie took a private jet to Cabo on Friday morning from Van Nuys Airport (in Los Angeles). It was a quick trip in honor of Katie's birthday. It was only them and two pilots on the plane," a source said.
"They stayed in one of the most private suites at the hotel. They wanted to be very discreet and had everything delivered to their room and taken care of by a personal butler," the source added.