The fourth preseason opponent will be the Jacksonville Jaguars.
Exact dates and times for the preseason will be announced later, but the Dolphins will open at home against the Super Bowl champion Tampa Bay Bucs on the weekend of Aug. 7-11.
The Dolphins then will travel to Jacksonville on the weekend of Aug. 14-18 before hosting Michael Vick and the Atlanta Falcons on the weekend of Aug. 21-25.
The preseason will wrap up with the trip to New Orleans on the weekend of Aug. 28-31.
Williams played briefly against the Saints last summer when the teams met in a preseason game at Pro Player Stadium. He gained 17 yards on eight carries that night in a game the Saints won 24-7.
The Dolphins also played Tampa Bay last preseason, with the Bucs winning 14-10 at Raymond James Stadium.