It received a lot of criticism.
"Instead of people just saying, 'Hey, I don't like that song,' all of a sudden they call you names. 'You're a redneck, you're a right-winger, you're automatically a Republican. You're automatically all these things," he told CBS News.
Keith says he wrote that song in 20 minutes, just days after the attacks — partly as a tribute to his father, who was a veteran. It's subtitled "The Angry American," and it doesn't mince words.
His connection to the military is evident as he gives a shout out to the military every show.
"I wanna thank the boys and girls proud enough and brave enough to wear our country's uniform wherever they are in the world tonight," he said at a recent show.
And part of that patriotism is the fighting spirit he's carried through his life. He's just as angry about 9/11 today as he was when he wrote his most famous song about 10 years ago.
"We're at war with the terrorists," he said. "And that if we don't try to do something about it, then it's gonna keep happening here until some of our freedoms are lost."
Keith won’t let politics get in the way of his music.
"It's amazing how many Republicans call me for support. And then they go, 'You're a Republican right?' And you go, 'Well I'm actually a lifetime Democrat,'" he said. "And then they go, 'Oh, sorry.' And the Democrats want so bad — the real liberals really want to hate me. And then they go, 'I still hate you, but I can't believe you're a Democrat.' So I'm not a real political guy. I'm a very patriotic guy."