Sheridan had been the team's linebackers coach the past four seasons. Spagnuolo, who held the job the past two seasons, left to become head coach at St. Louis.
"He does an excellent job of teaching, of reinforcing what we aspire to be with our defensive team," Coughlin said of Sheridan on the club's Web site. "Continuity is important to me, but the strength of staff is important, too. We've lost Steve, our coordinator, but it takes many, many people to be successful and to function properly. There was great harmony on that side of the ball. I want to keep that, I want to keep the continuity, I want the players to know that the fact they have performed to a high level the last two years is, in a way, being rewarded."
Coughlin noted secondary coach Peter Giunta also was considered for the position. Giunta was defensive coordinator for the St. Louis Rams when they won Super Bowl XXXIV.