The length of the players' contracts and financial terms were not disclosed.
Lofton, 28, was released by the New Orleans Saints this week, saving the team more than $4 million in cap space. He had 144 total tackles last season for New Orleans, his sixth straight season with 100 or more tackles.
Lofton, the Saints' leading tackler in 2014, has not missed a game in his seven seasons in the NFL with the Saints and Atlanta Falcons.
Williams was selected by the Arizona Cardinals in the first round of the 2010 NFL draft. He had 32 total tackles and one sack last season. In 70 career games, Williams has 157 total tackles and two sacks.
- Scooby Axson