Townsend, 34, played 12 seasons with the Pittsburgh Steelers after being drafted in the fourth round of the 1998 draft.
The 5-foot-10 Townsend has 21 career interceptions in 183 games.
He said earlier this month that he was surprised when the Steelers didn't re-sign him.
"I did kind of expect to be back, just to add some depth at the position," he said, according to the Pittsburgh Tribune-Review. "They know there's a player out there they don't really have to teach the system, that can come in and play."