Henderson has just impressed during a similar period with League One side Shrewsbury Town, and United have rewarded the England Under-21 international with a new contract.
Wilder told the club's official website: "This is a big one for us. Dean was certainly a target for rival clubs in our division.
"Dean is a confident boy, who has proved himself wherever he has been. He had a fantastic season for Shrewsbury, playing a starring role in what they achieved last year."
Henderson becomes the second-tier side's first signing of the summer.