The 26-year-old heiress was booked late Sunday into the Century Regional Detention Facility in an industrial area about five miles (eight kilometers) southeast of downtown Los Angeles, according to the sheriff's inmate locator Web site.
Though a judge sentenced her to 45 days behind bars, Hilton was expected to serve only 23 days because of a state law that requires shorter sentences for good behavior.
Earlier Sunday, Hilton attended the MTV Movie Awards, where she briefly spoke to reporters about her sentence.
"I am trying to be strong right now," Hilton said. "I'm really scared but I'm ready to face my sentence."