Jackson was controversially released by the Philadelphia Eagles last month after reports emerged linking him to a Los Angeles gang and calling his attitude off the field into question.
The 27-year-old was quickly snapped up by the Redskins, and Cofield was the latest team captain to lend his backing to the move after Robert Griffin III and DeAngelo Hall had already defended Jackson.
"A guy I absolutely hated playing against for eight years and a guy that hurt my teams countless times. So I was very excited getting him," Cofield told reporters.
Jackson enjoyed arguably the best season of his career last year, making 82 receptions for 1,332 yards and nine touchdowns.