I initially thought that the question concerned "enlisted" (not commissioned officer) fighter pilots, but it seems from the answers that the question was interpreted as how many USAAF pilots served as fighter pilots, with "enlisted" meaning "served."
Based on my interpretation of the question, I have been unable to determine how many enlisted (vs. commissioned) fighter pilots there were, but I am sure that information is available. The National Museum of the USAF says that "Between the world wars, at least 263 enlisted pilots served in the Air Corps" and that during WWII, "about 4,150 pilots trained and flew not as commissioned officers but as enlisted men -- almost 3,000 rated pilots and nearly 1,150 liaison pilots."
1920-1939: Between the Wars
The enlisted pilot program was developed since there were not enough young men with at least two years of college available for pilot training. "2,576 enlisted men are known to have graduated as sergeant pilots under this program. Ultimately they flew virtually all types of AAF aircraft. Although most were elevated to the new rank of flight officer with officer privileges or to second lieutenant before assignment to a combat unit, about 332 pilots departed the United States while still sergeants and about 217 flew combat missions overseas as sergeants. Not counted in this number are other sergeant pilots based in the United States flying antisubmarine combat patrols . . . Half of the first graduating class of flying sergeants went overseas with the P-38-equipped 82nd Fighter Group. Members of this class shot down 130 enemy aircraft, and nine became aces. In all, former sergeant pilots destroyed 249.5 enemy aircraft and 18 became aces flying fighters. "
https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196406/1941-1945-world-war-ii-sergeant-pilots//