The team also announced that it would tender contracts to its three- to six-year players eligible for arbitration. That group includes shortstop Ronny Cedeno and relievers Michael Wuertz and Kevin Gregg.
General manager Jim Hendry has never gone to arbitration with a player during his tenure, and was expected to reach agreements with Cedeno, Wuertz and Gregg.
Friday was the deadline for teams to decide whether to tender contracts to arbitration-eligible players who have three to six years' service time. Players not tendered a contract become free agents.
Johnson, who turned 32 on Monday, was one of the surprise success stories for the Cubs last season. He was released by the Blue Jays in late March, signed by the Cubs, and batted .303 with six homers and 50 RBIs in 109 games.
"Reed was a terrific contributor last year," Hendry said on Thursday. "I felt I'd failed all winter [after the 2007 season] to acquire a right-handed-hitting outfielder who could play center."
Scout Mark Servais saw Johnson last spring and called in reports saying that he was playing center, doing well and seemed to have recovered from the back problems that limited him to 79 games in 2007.
"I'd been trying to get some guys who, in hindsight, would've been lesser additions," Hendry said. "We had all our homework done, and we were reading [in] the papers that Shannon Stewart might be kept and Reed might be released. I think [Johnson] got released at eight in the morning, and we called at 8:05."
On Friday, Johnson signed a $3 million contract, and he could platoon in center with Kosuke Fukudome.
Gaudin, who inked a one-year, $2 million contract on Friday, was limited to eight appearances with the Cubs in the final six weeks of the 2008 season because of back problems. He was acquired as part of a six-player deal on July 8, along with Rich Harden, and went 9-5 with a 4.40 ERA for the season.
Cotts, 28, who agreed to a one-year, $1.1 million deal, went 0-2 with a 4.29 ERA in 50 relief appearances for the Cubs in 2008. He and Sean Marshall are the only left-handers in the bullpen as of now, but the team has hinted strongly that it would like to get Marshall into the rotation.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.