Mills, who was in the final year of a three-year contract, went 171-274 in 445 games as manager. The Astros lost a club-record 106 games last year and ensured themselves of a losing season Saturday by falling to 39-82, which is the worst record in baseball.
"I love the players, I love the effort they gave every day," he said. "They've been great to me and how they've gone about everything, and I love our fans. The fans we have here in Houston are the best, and they've been great to me, as well. I appreciate them an awful lot, and I wish the best for the players and the fans as we move forward."
Under the leadership of owner Jim Crane, who took control of the club late last year, and first-year GM Luhnow, the Astros have made wholesale changes throughout the organization, so it's no surprise the new regime would want to bring in a new manager at some point.
The Astros are in rebuilding mode and have traded several veterans for prospects in an effort to build toward the future. The club traded away Lance Berkman and Roy Oswalt in 2010, Hunter Pence and Michael Bourn last year and Carlos Lee, Wandy Rodriguez, Brett Myers, Chris Johnson and Brandon Lyon this year.
Mills, who was hired by former GM Ed Wade prior to the 2010 season after spending six years as bench coach of the Red Sox, was asked if he felt he had a fair chance to show what he can do as a manager on a rebuilding club.
"Every day, we tried to get the players the best they possibly could, and that was the goal every time out," he said. "We wanted to get them better; we wanted them to play well. Sometimes it just didn't work out, and if I'm going to sit here and point fingers, that's not right. There's some responsibility on my part as well."
Barnett joined the Astros prior to the 2011 season, replacing Jeff Bagwell. Houston's offense is ranked 15th in the National League in batting average and 14th in runs scored.
"When club is going as bad as we've been going, you kind of feel it every day that there might be something coming like that," Barnett said. "That's part of this side of the business, and you have to realize it and deal with it, and it's unfortunate. It's frustrating because I love the players. As tough as it's been, the biggest thing for me is the way these guys have gone about their business every day, conducted their work and tried to get better every day. That's a credit to them."
Barnett, who had previously served as hitting coach in Toronto and Kansas City, was a tireless worker and was a mentor to many young players who came up the last two years.
"They're young players, and they're trying to get better, and you get to a certain point in baseball that you're going to be the guy that's going to go down for it," he said. "That's what happened, but I appreciate the Astros giving me this opportunity and have really enjoyed it. I would have like to have been here to see this thing through to the other side of it."
Mills' thoughts were immediately about spending time with his family, including his son, Beau, who's a player in the Reds' system.
"We're going to move forward with some things and see what happens," he said. "The biggest thing is I'd like to go see my son play. For years, I've never really gotten an opportunity to watch him play and I want to see my daughter-in-law and see my granddaughter and watch him play a little bit and go from there."