By the mid-1930s they were discontinued in favor of telephone books and Yellow Pages.
City directories began to appear right after the American Revolution in larger cities and eventually spread to counties and towns. They were published yearly in most locations.  By the mid-1930s they were discontinued in favor of telephone books and Yellow Pages. City directories are an excellent way to track the movements of people between census years and to separate people with the same name by using addresses and occupations as identifiers.