BBC Radio Sheffield have made the announcement tonight. Henderson said: "I haven't taken a gamble coming to Sheffield United because this is a massive club."
Henderson joins new signings Greg Halford and Sun Jihai in Blackwell's summer transfers.
Blades boss Kevin Blackwell said: "I'm delighted and Darius is someone who I have been tracking for quite a while. When Rob took the opportunity to go to Derby their was only one player in my mind to replace him and that was Darius.
"He brings us quality of knowing how to get us into the Premier League. He knows what It's about and he's a lad who knows what It's like working for a living and I think he fits right into the Blades ethos."
Even more interviews from Henderson himself and Blackie coming up!
More to follow...