Five men have been jailed for the plot to attack the tower
The leader of a group which plotted to blow up the Sears Tower in Chicago has been sentenced to 13-and-a-half years in prison.
Narseal Batiste, 35, also planned to bomb FBI offices, along with four other men who have already been jailed.
Prosecutors said the men conspired to provide material support to al-Qaeda but defence lawyers said the plot was never serious.
Prosecutors in Miami had sought the maximum 70-year sentence for Batiste.
But he maintained he only went along with the plot to seize the $50,000 (£30,000) offered by an undercover FBI agent posing as an al-Qaeda operative.
The men, most of whom have Haitian backgrounds, were arrested in Miami in 2006.
They had been caught on tape by the FBI informant discussing plans to cause an anti-government insurrection.
Batiste was heard on audio and video tape saying they should start a "full ground war" that would "kill all the devils".
Sentencing Batiste, US District Judge Joan Lenard said: "You've done great harm to yourself, your family, the young men who were your followers, and you've violated the trust of your country."
Batiste apologised for the plot in court, saying he had "wanted respect".
"I wanted to be this person that I really wasn't. I've never been a violent person," the Associated Press news agency quoted him as saying.
On Wednesday, Judge Lenard sentenced brothers Burson Ausgustin, 24, and Rotschild Augustin, 26, to six and seven years in prison respectively.
The next day, Patrick Abraham, 30, received more than nine years and 34-year-old Stanley Phanor, eight years.
Two men were earlier acquitted of the charges.
The case was seen as a major step in the fight against extremist attack, but defence lawyers said the arrests were an overreaction by the authorities and that the men had no way of carrying out the plot.
"No one in the United States was ever in any danger. There were absolutely no steps taken to wage war," lawyer Ana M Jhones told AP.
The 110-storey Sears Tower, the tallest building in the US, was renamed as the Willis Tower this year.