The addition of Callahan comes one day after it was announced Florida defensive backs coach Travaris Robinson was returning to his alma mater, Auburn, as cornerbacks coach. Robinson's move reunited him with former Gators coach Will Muschamp, who was hired last month as Auburn's defensive coordinator.
It's a return to Gainesville for Callahan, who was a graduate assistant for the Gators from 2010-11. He was then hired by the Knights.
Callahan, 29, played defensive back for UCF from 2003-06. He was a student assistant in 2007 and then a graduate assistant the next two seasons at North Carolina.
A noted recruiter, he will be depended on in the Tampa, Fla., area, where his father, Sean, is the longtime head coach at Armwood High School, a perennial power.
Callahan's hiring is the latest in a slew of acquisitions for McElwain, who was named Florida's head coach last month. Two days before Christmas, McElwain hired former Michigan offensive coordinator Doug Nussmeier. McElwain has also brought in former Mississippi State defensive coordinator Geoff Collins, Western Kentucky running backs coach Greg Nord and Oakland Raiders defensive line coach Terrell Williams.
McElwain was hired last month from Colorado State, where he had a 22-16 record in three years, including a 10-2 mark this season. He replaces Will Muschamp, who had a 28-21 record in four seasons with the Gators.
Contributing: Will Green