Final answer:
The 1920 census revealed that a majority of Americans were living in cities.
Step-by-step explanation:
The census that first revealed that a majority of Americans were living in cities was the 1920 census. This census marked a significant shift in demographics as the urban population surpassed the rural population for the first time in U.S. history. Prior to 1920, the majority of Americans had been living in rural areas.
Learn more about Urbanization in the United States