The father of one of the defendants, 20-year-old Connor Stevens, complained to the judge that his son had been entrapped.
"My son is guilty," James Stevens said, "and so is the government."
Prosecutors had described the suspects as self-proclaimed anarchists who acted out of anger against corporate America and the government.
All three defendants - Stevens, 26-year-old Douglas Wright and 20-year-old Brandon Baxter - apologized in court. Their attorneys said the sentences would be appealed.
Wright, an Indianapolis man authorities called the ringleader, received the toughest sentence, 11 1/2 years. He apologized to his family and the community, saying he was an addict and needed help for substance abuse, not just prison.
Baxter, of Lakewood in suburban Cleveland, was given nearly 10 years in prison. Connor Stevens, of Berea, the least involved of the trio, was sentenced to more than eight years.
U.S. District Judge David Dowd had ruled last week that the men should be sentenced as terrorists, making them subject to harsher prison terms. After leaving prison, all three will be on supervised release for the rest of their lives.
A fourth defendant is being sentenced Wednesday, and a fifth is undergoing a psychiatric exam.
Stevens' mother, Gail, broke into tears and stopped reading a prepared statement. She portrayed her son as a gentle soul who shooed flies out of the house instead of killing them.
Brandon Baxter's father, Andy Baxter, challenged the government's case and mentioned his own battle with alcohol abuse. He told the judge his son had "a heart of gold, and please make this as light as possible."
Stevens, Baxter and Wright pleaded guilty to conspiring to use a weapon of mass destruction, knowingly attempting to use a weapon of mass destruction and attempting to damage property with explosives. There was no plea deal that would have reduced their sentences.
Last week, Dowd backed a government request to consider stricter sentences based on a "terrorist enhancement" for the trio. The ruling that the three were trying to intimidate the government expanded possible sentences from five or six years to 15 to 30 years or more.
The men were arrested by the FBI and had targeted a bridge over Cuyahoga Valley National Park between Cleveland and Akron. The FBI has said that the public was never in danger and that the device was a dud provided by an informant.
The defense called the case entrapment, with the informant guiding the way, and said the plot was more an act of vandalism than anti-government terrorism. They asked for sentences in the range of five years.
The government said the plot "was meant to convey a message to the civilian population, the corporate world, the financial system, and all levels of government."