ACR X RWY INCURSION TAXI INTO POS ON WRONG RWY CAUSED ACFT GAR.

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CHICAGO O'HARE GND CTL CLRED X TO TAXI TO RWY 4L VIA THE 'SILVER-ONE' TAXI RTING. THE CAPT AND I DISCUSSED THE WRITTEN INSTRUCTIONS FOR THE SILVER -ONE RTING AND PROCEEDED TO TAXI TOWARD RWY 4L. AFTER STARTING THE SILVER-ONE RTING AT TXWY INTXN A6; WE TURNED R ONTO TXWY B INSTEAD OF TXWY J. O'HARE GND CTL DETECTED OUR ERROR AND PROVIDED INSTRUCTIONS TO REPOS THE ACFT ONTO TXWY J. AS WE TAXIED ON TXWY J WE CONTINUED RUNNING THE BEFORE TKOF CHKLIST; 'DOWN TO THE LINE.' AS WE APCHED THE TXWY W INTXN; I LEFT THE COCKPIT TO CONDUCT THE PREDEP CONTAMINATION CHK IN ORDER TO INSURE THE WINGS WERE CLR OF SNOW ACCUMULATION. UPON RETURNING TO THE COCKPIT; I FAILED TO DETECT THAT WE HAD NOT TURNED R ONTO TXWY W. WE WERE HOLDING SHORT OF RWY 9L INSTEAD OF RWY 4L. AS I RETURNED TO THE COCKPIT; 'O'HARE TWR CLRED US 'ON TO HOLD' RWY 4L AND WE TAXIED INTO POS ON RWY 9L. AS THE CAPT TURNED ONTO THE RWY; HE REALIZED OUR MISTAKE AND IMMEDIATELY ADVISED TWR WE WERE IN POS ON RWY 9L. TWR SENT AN ACFT ON APCH FOR RWY 9L AROUND AND GAVE US INSTRUCTIONS TO EXIT RWY 9L AND REPOS FOR RWY 4L. WE CLRED THE RWY AND SUBSEQUENTLY DEPARTED RWY 4L WITHOUT FURTHER INCIDENT. I BELIEVE CONTRIBUTING FACTORS TO THIS INCIDENT ARE: 1) LACK OF FAMILIARITY WITH CHICAGO TXWYS. 2) NIGHT. 3) SNOWING. 4) A SUBTLE PRESSURE TO GET IN LINE AND DEPART PRIOR TO EXCEEDING OUR DE-ICING HOLDOVER TIME. 4) FATIGUE -- 10 1/2 HRS INTO A 14 HR CREW DUTY PERIOD.