The very first day of prayer was declared in 1775 by the Continental Congress, which asked people to pray for the fledgling nation. This initial declaration gradually evolved into two formalized events. In 1863 President Lincoln oversaw the naming of the autumnal observance of prayer and thanks as Thanksgiving Day.
Almost a century later President Truman oversaw the establishment of the spring tradition of prayer and thanks as the National Day of Prayer in 1952. The intent of the Day was to honor the history of public prayer in the United States by designating a day for Americans to come together and pray or meditate according to their own belief systems.
In 1988, President Reagan amended the 1952 resolution to designate that the National Day of Prayer would be on the first Thursday in May. Every year since then, the sitting U.S. President, regardless of party or denomination, has issued an official proclamation on the National Day of Prayer. Similarly, each of the 50 U.S. Governors issue annual proclamations. Many religious, interfaith, and community groups hold events recognizing the day.
While the U.S. government officially recognizes the day, it does not mandate or provide any guidelines as to how the day should be observed. Organizations and people from any tradition can create a National Day of Prayer observance, including interfaith groups. Anyone can organize an event, from a prayer breakfast to a food drive to a moment of silence.
In some places, a local Chamber of Commerce or service organization (e.g., Kiwanis) may organize a day of community service or similar type of charitable event to celebrate the day. Individual temples, churches, mosques, gurdwaras, or other houses of worship may hold their own events or come together for an interfaith event.
Sourced from https://tanenbaum.org/wp-content/uploads/2023/02/2023-National-Day-of-Prayer-Fact-Sheet.pdf