Steve Whitmore, a spokesman for the Los Angeles County Sheriff's Department, which runs the Century Regional Detention Facility in suburban LA, told the Associated Press that "her demeanor was helpful, she was focused, she was cooperative."
Whitmore said Paris, 26, had the usual jail breakfast on Monday: cereal, bread and juice.
Paris's mother, Kathy Hilton, who brought her daughter to the facility on Sunday night, is trying to be resolute, according to Hilton's publicist, Elliot Mintz.
Mintz told the New York Post that "Kathy is very emotional. She wanted to exhibit strength for her daughter."
Mintz added, "She thought it was the most important thing to do. She thinks Paris will emerge from this a better person. It's only been a day."
She is in the "special needs" unit of the jail, which contains 12 cells reserved for high-profile inmates. Each cell is 12'x8' with a small window, table, toilet, washbasin and two bunk beds – though Hilton is alone, reportedly to prevent any cellmate from selling a story about the experience of spending time with the heiress.