In order to help pay for its war effort in the American Civil War, Congress imposed the first personal income tax in 1861. It was part of the Revenue Act of 1861 (3% of all incomes over US $800 were taxed). This 1861 Act was rescinded in 1872.

Beginning in 1913, the 16th Amendment to the U.S. Constitution made the income tax a permanent fixture in the U.S. tax system. The amendment gave Congress legal authority to tax income. It resulted in a revenue law that taxed incomes of both individuals and corporations.

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