On August 1st, 1861 the U.S. Congress took up debate on a law that would create the first federal income tax. It set the rate at 3% for all incomes between $660 - $10,000 and 5% for those incomes over $10,000.
In 1864, the tax was increased to 5% on the former, and 10% on the latter.
I had this in some notes, but I do not have the original source indicated - too cool not to share, though. :)