The First Federal Census was conducted in 1790: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, Pennsylvania, Maryland, Virginia, North Carolina and South Carolina. Results showed that nine out of ten Americans were engaged in farming and food production.
This researcher has found a particularly useful tool. A booklet was reprinted from A Century of Population Growth, first published by the U S Government Print Office in 1909. It lists all the surnames and their variations, which were represented by at least 100 white persons in the U.S. in 1790. The newer publication lists 5700 surnames, average size of the family, total number of households, total number of members and the breakdown per state. It was released through THE RESEARCHER’S BOOKSHELF, Division of Heritage Quest and is called Surnames Listed in the 1790 United States Census.
A data sheet of O’Donoghues and variants taken from the 1901 Census.
The reference column puts entries into families but you would be advised to check the 1901 Census web pages for confirmation.