Coach Lovie Smith said the move had been building over several weeks because of sub-par play.
"We don't all of a sudden wake up one morning and just say, `Hey, we're going to go this direction,"' Smith said. "It's a pattern and I feel good about the decision that we had to make."
"We have young guys that we have in our starting lineup that we like," Smith said. "We'll see how they play. We feel pretty confident that they'll play good football."
Smith has maintained that Harris couldn't help the team on special teams, so he was less valuable than other safeties if he wasn't in the starting lineup.
Harris was in his second stint with the Bears after he was traded back from Carolina last year for linebacker Jamar Williams. After tying for the team lead in interceptions with five last season, Harris started the opener against Atlanta but missed the next three games due to a pulled hamstring.
Harris later added: "This Business known as the #NFL is a strange one. Chicago I want to thank u for all the luv u have shown me over the yrs. u will b missed."
Former teammates expressed surprise at Harris' departure. Defensive back D.J. Moore thought asking for a trade probably didn't help Harris' situation.
"I feel like once you say, `OK, I want a trade, I want something like that,' somebody (with the team) is feeling like he's trying to one-up me or something," Moore said. "It might be one of those things."
Smith called it a personnel move and not an attempt to send a message to other players about what can happen if they request trades.
Because Harris was released after the league's trade deadline, he is subject to waivers, reported NFL.com senior writer Steve Wyche. Harris could clear waivers by 4 p.m. ET Friday if he isn't claimed by another team, according to his agent.
The Associated Press contributed to this report.