The Cowboys had spent their first three picks of the draft on defensive players, trading up for LSU cornerback Morris Claiborne at pick No. 6 overall, then adding Boise State defensive end Tyrone Crawford with their lone pick in Friday night's third round. The first of Saturday's two fourth-round selections was used on Wake Forest outside linebacker Kyle Wilber.
Johnson (6-1, 212) has been timed in the low 4.5-second range in the 40-yard dash, and is considered a solid, physical tackler with some coverage ability. He had 17 career interceptions, one shy of the school record, starting every game in which he played.
He had recorded an interception in each of his first two games as a senior in 2011, but was forced to miss most of the season after suffering a biceps injury in October.