March 31, 2025 is not a federal holiday in the United States. It is a Monday and most businesses, schools, and government offices will be open.
However, some states and localities may observe March 31 as a holiday. For example, in the state of Hawaii, March 31 is known as Kamehameha Day and is a state holiday. Kamehameha Day commemorates the birth of Kamehameha I, the founder and first king of the Kingdom of Hawaii.