The UN agency said it identified 3,206,736 internally displaced Iraqis (534,456 families) from then through September 29 of this year.
Of those, 42 percent were from the western province of Anbar, the statement added.
Fighting continues on several fronts in Anbar, where a major government operation to recapture the provincial capital Ramadi from the Islamic State group is under way.
"Displacement in Iraq continues to increase; displaced people are in need of comprehensive support; most fled their homes with only what they could carry," said IOM's Iraq chief, Thomas Lothar Weiss.
There are 7.6 million displaced people in neighbouring Syria. More than four million fled the country, including about 250,000 to Iraq.
The world is grappling with its worst refugee crisis in 70 years, and UN chief Ban Ki-moon said recently the world body's humanitarian agencies were "broke".
Appeals for both Syria's and Iraq's emergency response plans are massively under-funded.
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