The first "cocktail party" ever thrown was allegedly by Mrs. Julius S. Walsh Jr. of St. Louis, Missouri, in May 1917. Mrs. Walsh invited 50 guests to her home at noon on a Sunday. The party lasted an hour, until lunch was served at 1 pm. The site of this first cocktail party still stands. In 1924, the Roman Catholic Archdiocese of St. Louis bought the Walsh mansion at 4510 Lindell Boulevard, and it has served as the local archbishop's residence ever since.
During Prohibition in the United States (1920–1933), when the sale of alcoholic beverages was illegal, cocktails were still consumed illegally in establishments known as speakeasies. The quality of the alcohol available was far lower than was previously used, and bartenders generally put forth less effort in preparing the cocktails. There was a shift from whiskey togin, which does not require aging and is thus easier to produce illicitly.