The hospital's statement Friday provides the first details about the congressman's whereabouts and condition since he mysteriously went on a medical leave from Congress several weeks ago.
The hospital says he's undergoing an extensive inpatient evaluation for depression and for gastrointestinal issues.
The Mayo Clinic's statement didn't address Jackson's previous whereabouts. But it said the congressman, the son of civil rights leader Jesse Jackson, and his family are "grateful for the outpouring of support and prayers."
Jackson has been on medical leave since June 10.
Jackson's staff about two weeks ago announced he was suffering from a "mood disorder."
Jackson's office released what they said was his doctor's statement. It read, "The Congressman is receiving intensive medical treatment at a residential treatment facility for a mood disorder. He is responding positively to treatment and is expected to make a full recovery."
While Jackson's anonymous doctor expects the congressman to recover, he or she did not set a timetable for it.
Medical experts say mood disorders can range from major depression or even bipolar disorder.
"Mood disorder is as vague as exhaustion and it's obviously hiding some truth that's much more serious and much more damning to his political career," said ABC7 political analyst Laura Washington.
The Associated Press contributed to this report.