Federal income tax was introduced with the Revenue Act of 1861 to help fund
the Civil War, and subsequently repealed, re-adopted, and held unconstitutional.

The early taxes were based on assessments, not voluntary tax returns. Tax
payment dates varied by act.

Since 1955, for those living in the United States, Tax Day has typically fallen on
April 15. For those filing a U.S. tax return but living outside the United States and
Puerto Rico, Tax Day has typically fallen on June 15, due to a two-month automatic 
extension granted to filers by the IRS.