CARGO MLG MAKES WRONG ARPT APCH DURING A NIGHT OP.

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APCHING STEWART INTL; NEWBURGH; NY; AT EARLY MORNING TWILIGHT HRS AT 4000 FT MSL. THE ACFT WAS APCHING STEWART INTL FROM THE NE ON A VECTOR FOR STEWART. THE ACFT WAS IN AND OUT OF CLOUDS SKIMMING THE BOTTOM OF THE CLOUD LAYER. IT WAS ABOUT 5 NM VISIBILITY BELOW THE CEILING. UPON SIGHTING WHAT THE CAPT AND I THOUGHT WAS STEWART INTL; THE CAPT ASKED APCH FOR LOWER SO WE COULD GET BELOW THE CEILING AND MAINTAIN VISUAL ON THE FIELD. APCH APPROVED A DSCNT TO 3000 FT. UPON GETTING BELOW THE CEILING THE CAPT RADIOED APCH THAT FIELD WAS IN SIGHT. APCH CLRED THE ACFT FOR A VISUAL TO RWY 9 AT STEWART INTL AND ADVISED US TO SWITCH TO STEWART TWR. UPON CIRCLING JUST PRIOR TO ROLLING ON FINAL AT APPROX 1500 FT AGL STEWART TWR ADVISED US WE WERE LINED UP ON RWY 6 AT DUTCHESS COUNTY ARPT. THE DUTCHESS COUNTY ARPT TWR WAS CLOSED AT THE TIME. WE SWITCHED BACK TO APCH FOR A VECTOR BACK TO STEWART INTL. PERFORMED A VISUAL APCH AND LNDG AT STEWART INTL RWY 9 WITHOUT FURTHER INCIDENT. CONTRIBUTING FACTORS WHICH LED TO MISIDENTING DUTCHESS COUNTY ARPT FOR STEWART INTL: BOTH THE CAPT AND I HAD BEEN TO STEWART INTL ON OCCASION BUT HAD ALWAYS ARRIVED AT THE ARPT APCHING FROM THE W. THIS LED TO A FALSE SENSE OF SECURITY AND FAMILIARITY WITH THE FIELD WHEN APCHING FROM THE E. WHEN ASSIGNED A HDG FOR STEWART INTL BOTH NAV #1; NAV #2 WERE TUNED TO THE LOC RWY 9 AS THERE WERE NO NAVAIDS LOCATED ON STEWART. THIS LED TO A LOSS OF POS AWARENESS. APCH CTL ASSUMED WE HAD IDENTED THE CORRECT FIELD. THEY NEVER GAVE A DISTANCE; DIRECTION TO STEWART INTL; EVEN WHEN THE FIELD WAS CALLED IN SIGHT APPROX 4 NM NE OF DUTCHESS COUNTY ARPT APPROX 12 NM FROM OUR DEST OF STEWART INTL; WELL BEYOND THE PREVAILING VISIBILITY. STEWART INTL AND DUTCHESS COUNTY ARPTS ARE VERY SIMILAR IN APPEARANCE. FATIGUE MAY HAVE PLAYED SOME FACTOR. STEWART INTL WAS OUR FINAL DEST AFTER FLYING THROUGHOUT THE NIGHT.