National Tartan Day is a US observance on April 6 each year. It commemorates the Scottish Declaration of Independence, from which the American Declaration of Independence was modelled on. It also recognizes achievements of Americans of Scottish descent.

Librarians across the United States celebrate National Library Workers’ Day (NLWD) on the Tuesday of National Library Week, held in April every year.

Many United States residents mark Tax Day as the deadline to file their income tax details to the Internal Revenue Service (IRS). The date is usually on or around April 15. However, this deadline may be extended to accommodate holidays or extreme weather conditions.

The Boston Marathon is held in the city of Boston, Massachusetts on Patriot's Day, the third Monday of April. First held in 1897, it is the world's oldest annual marathon.

Administrative Professionals Day® highlights the important role of administrative professionals in all sectors of the modern economy worldwide. It is on the Wednesday of Administrative Professionals Week®, which is on the last full week of April.

Oklahoma Day, which is annually held on April 22, commemorates the date when the "Oklahoma Lands" area, which is now the state of Oklahoma, opened for European settlement.