U.S. District Judge Amy Berman Jackson, who is not related to Jackson Jr., also sentenced the former congressman's wife, Sandi, to a year in prison, the Chicago Tribune reported. The judge said Jackson Jr. will serve his sentence first so the couple's children will have one parent available.
Both the former congressman and his wife were convicted of misspending $750,000 in campaign funds.
"I am the example for the whole Congress," Jackson said, occasionally stopping to wipe away tears. "I understand that. I didn't separate my personal life from my political activities, and I couldn't have been more wrong."
Jackson's father, the Rev. Jesse Jackson, said later he was proud of his son. The longtime civil rights leader said recent months have been "filled with dark days and many low moments" for the family.
"Today I speak as a father. I was proud of Jesse Jr. as he stood before the judge and accepted full responsibility for his actions," he said. "He was remorseful. He is recovering. He has highs and lows. I have a greater appreciation for it now."
Jackson Jr. took medical leave in 2012 for what was later revealed to be for treatment of bipolar illness. He and his wife later admitted spending campaign funds on personal items that included an expensive Rolex watch, two elk heads and one of Michael Jackson's fedoras.
Spending sprees can be a symptom of bipolar illness, formerly called manic-depressive psychosis.
The elder Jackson said before the hearing his son's illness is genuine.
"I don't know how I missed so many signs," he said. "We found out he was sick very late. We thought we almost lost him. He was in a different place altogether."
The judge rejected Sandi Jackson's plea for probation, telling her, "It is not the court that put your children in this position."
Jackson Jr. -- who served in Congress for 17 years before resigning in 2012 -- said this month he intends pay a $750,000 forfeiture in 90 to 180 days.
Federal prosecutors were seeking a term of four years for Jackson and 18 months for his wife for failing to report approximately $600,000 in income on the couple's tax returns.