From a Newsweek poll:

Perhaps most alarmingly, 41% of Americans answered ‘Yes’ to the question “Do you think Saddam Hussein’s regime in Iraq was directly involved in planning, financing, or carrying out the terrorist attacks of September 11th, 2001?”

That total is actually up 5 points since September 2004.

Further, a majority of people couldn’t identify Saudia Arabia as the country of origin of most of the 9/11 hijackers, even given the question in multiple choice format. 20% answered Iraq, while 14% believed the hijackers came from Iran.