Monument Day commemorates the collapse of society in The Walking Dead universe. The fall occurred on Friday, August 27, 2010, three days after the Wildfire Virus became a global pandemic and the dead began to rise. Unrest and rioting lead to Martial Law being declared, and Operation Cobalt would be implemented two weeks later.

Operation Cobalt was carried out by the U.S. Military and ended after forces lost control and areas with large numbers of infected and large cities were bombed, in an attempt to contain the spread of the virus. According to Walking Dead story lines, at that point the government collapsed.

In the television series, Monument Day was first honored during The Walking Dead: World Beyond spinoff series at the Campus Colony in Lincoln, Nebraska, followed by Feast Day.