Dempsey flew in to hold talks with "Iraqi political and security officials on (the) next phase of the campaign to defeat (IS)," Brett McGurk, the number two US envoy for the coalition battling the jihadist group, said on Twitter.
The US is ramping up its efforts against IS, with President Barack Obama announcing plans to deploy up to 1,500 more US military personnel to the country to advise and train Iraqi forces, raising the total cap to 3,100.
A US-led coalition is carrying out air strikes against IS in Iraq, where the jihadists spearheaded a lightning offensive that overran much of the Sunni Arab heartland in June.
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The group also holds significant territory in Syria.
Iraqi security forces performed poorly in the initial days of the IS-led onslaught, when multiple divisions collapsed and the group seized large amounts of military equipment.
But helped by the air strikes, support from Shiite militias and Sunni tribesmen, and assistance from international advisers, Baghdad's forces have begun to make progress.
Iraq retook the strategic northern town of Baiji on Friday, the largest it has recaptured since the conflict began.
Baiji lies on the road to second city and IS hub Mosul, and its capture also further isolates militants who hold the city of Tikrit, to the south.