"Congressman Jesse Jackson Jr. has arrived at Mayo Clinic in Rochester, Minn., for extensive inpatient evaluation for depression and gastrointestinal issues," the statement, issued by the clinic, said.
"Further information will be released as Congressman Jackson's evaluation proceeds.
"Congressman Jackson and his family are grateful for the outpouring of support and prayers that have been received throughout his care."
The statement is more specific than previous reports about Jackson since June 10, when he went on medical leave, the Chicago-Tribune reported.
The statement did not say where Jackson, 47, had been before going to the Mayo Clinic, the newspaper said.
Jackson's office had said in June he was absent on medical leave for treatment for exhaustion. His office said in a statement July 11 he was receiving inpatient treatment for a "mood disorder," but did not say where. His office had not disclosed further information on his condition, citing medical privacy, the newspaper said.
The U.S. House Ethics Committee is investigating allegations a friend of Jackson's, Raghuveer Nayak, offered as much as $6 million in campaign funds to Rod Blagojevich -- who was Illinois' governor at the time but is currently serving a 14-year prison term for corruption. In exchange, Blagojevich was to appoint Jackson to the U.S. Senate seat vacated by Barack Obama after he was elected president.
Jackson has said he had no knowledge of the alleged matter.
Nayak was arrested in June, charged with fraud in the operation of his surgical centers, the Tribune said.