The Constitution provided that representatives should be distributed among the states according to population as modified by the federal ratio. To do this it was necessary to find out how many people there were in each state. In 1791 the first census was taken. By that time both North Carolina and Rhode Island had joined the Union, and Vermont had been admitted as the fourteenth state. It appeared that there were nearly four million people in the United States, or not as many as one hundred years later lived around the shores of New York harbor. There were then about seven hundred thousand slaves in the country. Of these only fifty thousand were in the states north of Maryland. The country, therefore, was already divided into two sections: one where slavery was of little importance, and another where it was of great importance.

The first new state to be admitted to the Union was Vermont (1791). The land which formed this state was claimed by New Hampshire and by New York. But during the Revolution the Green Mountain Boys had declared themselves independent and had drawn up a constitution. They now applied to Congress for admission to the Union as a separate state. The next year Kentucky came into the Union. This was originally a part of Virginia, and the colonists had brought their slaves with them to their new homes. Kentucky, therefore, was a slave state. Vermont was a free state, and its constitution forbade slavery.