PA-46 Malibu/Malibu Mirage/Malibu Matrix
Air Traffic Control Fully Certified
Distraction; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Human Factors
PA44 was inbound to ZZZ airport from the south. When the aircraft checked on frequency; I picked up the strip for a different aircraft and put it in front of me. The strip I was looking at said VFR; so I had it in my mind that PA44 was VFR.  Obviously I wasn't looking at either the strip or the Data Block on the aircraft closely enough. After flying about 10 or 15 miles toward ZZZ Airport at 100; PA44 said they had the airport in sight and asked if they could descend to 8;000. That's when the light came on and I realized that the aircraft was IFR. I had another aircraft; an IFR Citation coming in fast from the southeast and became focused on how I was going to make the sequence work. Without thinking; I gave PA44 what he had asked for; descent to 8;000 and a vector to follow the Citation. Several minutes later I realized what I had done: this guy was at 8;000 in a 9;000 FT MVA! I was horrified. By that time; PA44 was about to exit the 9;000 FT MVA for an 8;000 MVA. PA44 landed behind the Citation without incident. I'm not sure why I didn't have my head fully in the game; but I intend to be more vigilant from now on.
TRACON Controller described a below MVA event when handling an IFR aircraft as a VFR and issuing a descent to below MVA limitations.  The reporter listed lack of vigilance as the primary contributing factor.