The honest answer is both, depending on which version of the dish you are talking about. The original was invented in Rome. The version most people in the United States picture when they hear the name was largely developed in America.
The Italian Origin
Alfredo di Lelio created the original dish in Rome around 1907 to 1908. His version used fettuccine, a very generous amount of high quality butter, and aged Parmesan, with pasta water as the only other ingredient. It was an Italian dish, made by an Italian restaurateur, in Italy, with Italian ingredients. That part of its origin is not in dispute.
Where America Comes In
After American celebrities helped make the dish famous following their visit to di Lelio’s restaurant in 1927, American restaurants began creating their own versions. The key change was adding heavy cream, which made the sauce easier to hold and serve at scale. This cream-based version is the one that became standard across the United States and the one most people outside of Rome think of when they hear the name Alfredo sauce.
What Italian Cooks Think
In most of Italy outside of Rome, fettuccine Alfredo as a named dish is not particularly common or well known. Italian cuisine has dishes that cover similar territory, cacio e pepe, fettuccine al burro, and various regional butter and cheese pastas, but the cream-based American Alfredo is not considered a standard part of the Italian culinary tradition.
The Bottom Line
The name and the original concept are Italian. The cream-based version that became an American staple is largely an American development. Both versions are real dishes worth making. The original Roman version is covered in our authentic Italian Alfredo sauce recipe. The American version is our classic Alfredo sauce. For the full historical story, see our history of Alfredo sauce page.