Kilgallon, 23 has joined the Bramall Lane club on a three year deal and cost £1,750,000 and could rise to a further £250,000 if United retain their Premiership status.
The former Leeds defender has become Neil Warnock's first signing of 2007 whilst Kilgallon has some top flight experience; playing ten games before they were relegated.
The Defender told BBC Radio Sheffield; "Playing in the Premiership is what I've always wanted to do.
"Coming here gives me that chance. This is a big opportunity for me in the Premiership. I'm here now and I'm really excited about it.
"I've played well in the Championship, but now this is a step up, so I have got to prove myself.
"I played a few games in the Premiership when I was younger and I did okay, but now I have to show what I can do all over again.
"I'm 23 today, and now I want to establish myself as a good, young defender in the Premiership. I want to do as well as I can."