ON 1/31/83 AT 2134 CST, THE ACFT DEPARTED GRAND ISLAND, NE ON AN IFR FLT PLAN TO TOLEDO, OH, WITH APPX 125 GAL OF FUEL ON BOARD. WHILE EN ROUTE, THE PLT RECEIVED UPDATED WX FOR TOLEDO. AT THAT TIME, THE TOLEDO WX WAS INDEFINITE 100 FT OBSCD, VIS 1-1/2 MI WITH RAIN & FOG, PRESSURE FALLING RAPIDLY. THE PLT CHANGED HIS DESTINATION TO AN ALTN ARPT AT FT WAYNE, WHERE, AT THAT TIME, THE WX WAS 400 FT OVC, VIS 3 MI WITH LGT RAIN & FOG. BY THE TIME, THE ACFT HAD ARRIVED IN THE FT WAYNE AREA, THE CEILING HAD DROPPED TO 200 FT OVC. THE PLT WAS CLRD FOR AN APCH TO THE FT WAYNE MUNI ARPT. BY THAT TIME, THE TOWER WAS CLOSED, BUT THE RWY LGTS WERE SET ON BRIGHT. AT APRX 0212, THE ACFT COLLIDED WITH TREES THEN IMPACTED THE GND APRX 1.5 MI NE OF THE ARPT, ABOUT 3 HRS, 48 MIN AFTER TKOF, ON A HDG OF 120 DEG. AN EXAM OF THE ENGINE REVEALED NO DISCREPANCIES THAT WOULD HAVE PREVENTED NORMAL OPERATION. THERE WAS EXTSV DMG TO THE FUEL SYS, THE AMOUNT OF FUEL ON BOARD BRF IMPACT WAS NOT DTRMD, BUT A PAX RPRTD 4 HRS OF FUEL & A RESERVE.