* New Year's Day, January 1st.
* Birthday of Martin Luther King, third Monday in January.
* Inauguration Day, January 20th every four years, starting in 1937.
* Washington's Birthday, third Monday in February since 1971; prior to that year, it was celebrated on the traditional date of February 22.
* Inauguration Day, March 4th every four years, pre-1937.
* Armed Forces Day, third Saturday in May.
* Memorial Day, last Monday in May since 1971; from 1868 to 1970 it was celebrated on May 30, and was called Decoration Day for part of that time.
* Flag Day, June 14th.
* United States of America's Independence Day, July 4.
* Labor Day, first Monday in September.
* Columbus Day, second Monday in October (federal holiday since 1971).
* Election Day, Tuesday on or after November 2.
* Veterans Day, November 11th (except from 1971 to 1977, inclusive, when it was celebrated on the fourth Monday in October; formerly known as Armistice).
* Thanksgiving Day, fourth Thursday in November.
* Christmas Day, December 25th. I have finally included this since it is a federal holiday, although it is not based on a secular holiday.
* Groundhog Day, February 2.
* Lincoln's Birthday, February 12.
* Valentine's Day, February 14.
* Washington's Birthday, February 22.
* St. Patrick's Day, March 17.
* April Fools's Day, April 1.
* Earth Day, April 22 (since 1970; see Earthday.net)
* Administrative Assistants' Day, which once upon a time was Secretaries' Day, is the Wednesday of the last full week of April (that is, the Wednesday before the last Saturday in April) since 1955; see this site for more information.
* Arbor Day is often the last Friday in April (since 1872), but since planting conditions vary, it may occur from September to May; please consult the National Arbor Day Foundation's list of Arbor Day Dates.
* Mothers' Day, second Sunday in May (36 USC Sec. 142).
* Fathers' Day, third Sunday in June (36 USC Sec. 142a).
* Parents' Day, fourth Sunday in July (36 USC Sec. 142c).
* Grandparents' Day, Sunday after Labor Day (36 USC Sec. 142b).
* Columbus Day (traditional), October 12.
* United Nations Day, October 24.
* Halloween, October 31.
* Daylight Saving time begins, (currently) first Sunday in April (but not in Arizona, Hawaii, and most of the counties of Indiana).
* Federal Income Taxes are due April 15th; if the 15th is a Saturday or Sunday, then the due date is the Monday after the 15th.
* Daylight Saving Time ends, last Sunday in October (but not in Arizona, Hawaii, and most of the counties of Indiana).