Coach Jack Del Rio called Garrard's release "purely a football decision."
"As always, we seek to play with the best players and I think it's imperative we do what's best for the football team," Del Rio said.
Garrard, a 2002 Jacksonville draft pick, took over as the team's starting quarterback in 2007 when he replaced Byron Leftwich. He has thrown for 16,003 yards, 89 touchdowns and 54 interceptions with a 61.6 percent completion percentage. He has also run for 1,746 yards and 17 TDs. He started 76 of the 86 NFL games in which he has played.
Jacksonville opens its 2011 season Sunday at home against Tennessee.
McCown, originally drafted out of Louisiana Tech in 2004 by Cleveland and obtained from Tampa Bay two years ago, has only played in 16 NFL games, starting seven.
He has completed 154 of 260 passes for 1,739 yards with nine touchdowns and 10 interceptions for a 74.8 rating.