AN ACR CREW; AFTER LNDG AT ITO; TAXIED ON CLOSED PORTION OF RWY.

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RWY 8/26 AT ITO ARPT WAS NOTED TO HAVE 3000 FT OF CLOSURE ON THE W END DUE TO CONSTRUCTION. WE WERE VECTORED FOR AN ILS RWY 26 APCH DUE TO DECAYING WX CONDITIONS: LIGHT RAIN; 800-1000 FT CEILING WITH A SLIGHT TAILWIND. UPON LNDG; THE CREW NOTICED BARRICADES ACROSS (CONES) THE RWY AHEAD; AND ELECTED TO ROLL OUT TO THE LAST TXWY BEFORE THE CONED OFF SECTION OF THE RWY. WHILE SLOWING TO THE TXWY; TWR RADIOED TO US THAT WE HAVE ENTERED THE CLOSED SECTION OF THE RWY AND TO DO A 180 DEG TURN AND EXIT THE RWY VIA THE TXWY THAT WE JUST PASSED. WHILE TURNING AROUND ON THE RWY; WE THEN NOTICED SOME OTHER BARRICADES AND CONES THAT WERE PLACED ALONG THE SIDES OF THE RWY TO IDENT THE CLOSED SECTION. WE DID NOT NOTICE THESE IDENTIFIERS (CONES) ON LNDG ROLLOUT DUE PARTLY TO RAIN AND LOW VISIBILITY AND MOSTLY DUE TO THE FACT THAT WE HAD BOTH SEEN THE CONES AND BARRICADES ACROSS THE RWY FURTHER DOWN THE RWY AND BELIEVED THAT IDENTED THE CLOSED SECTION. I ASKED TWR IF THERE WAS A PROB WITH THIS INCIDENT AND HE STATED 'NO.'