Alan Leroy McVay, 47, of Medford, Oregon, was sentenced after pleading guilty to malicious destruction of property by explosion for the bombing last fall of the Jackson County District Attorney's Office.
A propane gas tank rigged to a detonator and hurled by McVay against a window of the building on Nov. 13 exploded in flames, shattering glass and damaging the brick exterior, authorities said. No one was hurt in the pre-dawn blast.
Police in Medford, some 475 miles south of Portland near the California border, said immediately afterward they considered the bombing an act of domestic terrorism.
Federal prosecutors said in a statement on Monday that McVay confessed when arrested a week later to committing the bombing in an attempt to destroy the prosecutor's office and delay a plea hearing and sentencing scheduled in state court for the next day.
He had been charged at the time with four residential burglaries and a firearms offense.
As part of his plea deal with federal prosecutors on the bombing, McVay also agreed to enter a guilty plea to the burglary-related charges in state court, with those sentences to be served concurrently with his 15-year federal prison term.
U.S. District Judge Owen Panner also ordered McVay to pay more than $14,000 in restitution to Jackson County for damage to the district attorney's office.