The first national census recorded a U.S. population of 3,929,214 in 1790.
The census was conducted under the Census Act of 1790, signed by President George Washington. Marshals began collecting information on August 2, 1790, using the population as of Census Day, and the enumeration covered the original states plus the districts of Kentucky, Maine, and Vermont and the Southwest Territory.
The census counted free people, enslaved people, and other persons under categories defined by the law. It did not attempt to measure the population using modern standards, and Native Americans living outside the tax system were excluded from the official count. The categories therefore reflected the legal and political structure of the early republic.
The result was important for representation because the Constitution required population counts to help apportion seats in the House of Representatives. The total is sometimes rounded to 3.9 million, but 3,929,214 is the detailed official figure commonly cited for the 1790 census.