The US military announced on Monday that a marine assigned to Regimental Combat Team 5 died of wounds sustained during fighting in the western Anbar province on Sunday.
The marine's name was being withheld while his family was notified.
October was already the worst month since January 2005 when 107 troops were killed.
The highest monthly toll was in November 2004 when 137 deaths were recorded.
Four non-American soldiers have also died in attacks during the month.
Opinion polls indicate that a growing numbers of US voters want to see the 140,000 US troops serving in Iraq return home.
Since the invasion which removed Saddam Hussein from power, a total of 2,813 US troops have been killed.
George Bush's Republican party could possibly lose control of Congress in elections on November 7, with opinion polls indicating that his policy on Iraq could influence voters against his party.