The nation is celebrating Peace Officers Memorial Day today by flying flags at half staff in remembrance of the fallen law enforcement officers who have made the ultimate sacrifice.

The day is marked during National Police Week, in which tributes remind the nation of the sacrifice of the 19,981 known fallen officers in U.S. history. The day is celebrated each May 15 and included President Obama meeting with the families of the fallen.

A historic crime bill signed by President Clinton in 1994 established the memorial day as a half-staff flag day at the request of the National Law Enforcement Officers Memorial Fund (NLEOMF). It's one of only two days, including Memorial Day, where government agencies, businesses and residents are asked to fly their U.S. flags at half staff.

"Lowering flags to half staff on Peace Officers Memorial Day is also a way to remember the family members, friends and colleagues these brave American heroes left behind," said Craig W. Floyd, the NLEOMF's chairman and CEO.

Peace Officers Memorial Day was initially designated on May 15 in 1962 by President Kennedy to fall during National Police Week. The names of 321 fallen officers were added to the national police memorial this year and honored during the annual Candlelight Vigil.