The big target (6-foot-3, 215 pounds) never lived up to the high expectations set for him after the Cowboys traded draft picks in the first, third and sixth rounds to the Lions for him in October 2008.
Williams, who played last season for the Bears, worked out for the Houston Texans this offseason but didn't receive a contract offer. The Miami Dolphins asked him to try out, but Williams decided he was done with football.
"There was no need for me to go back," Williams told the newspaper after announcing his retirement on Facebook. "It's hard to quit when you have been doing something the third grade. I'm in good shape. ... I can still play. But when I declined to workout in Miami, I knew I was done."
But Williams' career most likely will be remembered for what he didn't do on the field after being traded to the Cowboys.
Williams never surpassed 40 receptions in the three-and-a-half seasons after the trade and scored just 15 touchdowns in that time, too.
"Put up good numbers my first few years, went to a Pro Bowl then I got to Dallas and it stopped," Williams said. "It is what it is. God had a plan for me. The grass ain't always greener on the other side."
Williams finished up his career with the Bears in 2011, catching 37 passes for 507 yards and two touchdowns.