A 22-year-old patient of the Timberline Knolls Residential Treatment Center was reported missing Tuesday, according to Lemont police.

Kristen Longhi was last seen at the treatment facility around 12:40 p.m., before she told a nurse she was going for a walk, according to a release from the Lemont Police Department.

Police said Longhi is a psychiatric patient receiving care for bipolar disorder, and suffers from delusions and paranoia.

"What makes this case unique is the girl is a psychiatric patient, so we're being careful to respect her privacy while trying to find her," said Lemont Police Chief Kevin Shaughnessy. "I can say that her mother reported her missing and endangered."

Longhi is described as white, 5-foot-3-inches tall, 145 pounds, with brown hair and hazel eyes. According to police, she was last seen wearing a green coat, jeans and a purple stocking hat, and has an Indian tattoo on her top right foot. She may be in possession of a Visa gift card and a pair of glasses, police said.

According to Lemont police, Longhi has a history of walking away from treatment facilities, and has been previously located in Texas and Colorado. Shaughnessy said detectives are working with other law enforcement agencies, including police in Hobart, Ind., where Longhi lived prior to being admitted to Timberline Knolls in July 2010.

Timberline Knolls spokesperson Susie Lomelino declined to confirm or deny Longhi's disappearance, but said the facility was currently dealing with "a situtation."

“In regards to patient information, it is our policy to maintain strict levels of confidentiality," Lomelino said. "Privacy, safety and the well-being of our residents are our first priority, and we employ standards and policies that make this practice possible at all times, including providing support to families and authorities.”

Friends and family members have started a Facebook page called "In Search of Kristen Longhi." In a note posted Thursday morning, Longhi's mother, Maureen Smith, said her daughter is likely off her medications, which could cause seizures or other unpleasant symptoms.

Anyone with information should contact the Lemont Police Department at 630-257-2229.