Townsend will replace Ed Donatell, who left to become Vic Fangio's defensive coordinator in Denver after four years in Chicago.
Townsend was an assistant defensive backs coach for the Giants this past season. Prior to that, he worked for the Tennessee Titans (secondary coach in 2016-'17), Mississippi State (cornerbacks coach from 2013-15) and Arizona Cardinals (assistant defensive backs coach from 2011-'12).
Townsend is a 13-year NFL veteran.
Williams had a previous tie to the Bears, having worked on their coaching staff during training camp last summer. He then completed his second year as a defensive analyst at Temple in 2018.
He played collegiately at Division-II West Chester University.