Per Terez A. Paylor of the Kansas City Star, Amerson's contract with the Chiefs is for one year.
The Chiefs struggled to defend opposing quarterbacks last season. They finished 29th in passing yards allowed (3,952).
Marcus Peters and Steven Nelson are entrenched as starters for Kansas City's secondary, but the team went through a revolving door with Phillip Gaines, Kenneth Acker, Darrelle Revis and Terrance Mitchell as the No. 3 cornerback in 2017.
Amerson was originally drafted 51st overall by Washington in 2013. The 26-year-old has spent the past three seasons with the Oakland Raiders. A foot injury kept him out for the final nine games last season, though he still tied for fifth on the team with four passes defensed.