On Omaha beach, the 1st US Army infantry division had seen combat in North Africa and Sicily. This assault was reinforced by elements of the green 29th infantry division, that never saw combat before and nine companies of US Army Rangers. About 80 % of the Rangers had seen combat in 1942 and 1943, when they served with the 34th and 36th US Army infantry divisions, in North Africa, Sicily and southern Italy.
On Utah Beach, the 4th US Army Infantry division and the 5th Ranger battalion made their combat debuts on D-Day. Behind the beaches, the 82nd airborne division had seen combat in Sicily and during the Salerno landings of September 9th 1943. The 101st airborne division had not seen combat before June 6th 1944.
Roughly half of the troops that the US Army deployed on D-Day had combat experience from 1942 and/or 1943, gained in operations Torch in North Africa, operation Husky in Sicily or operation Avalanche, the invasion of Salerno in southern Italy.
Source: "There's a war to be won: The US Army in World War II" by Geoffrey Perret