The World Health Organization declared Liberia free of Ebola on Saturday, making it the first of the three hardest-hit West African countries to bring a formal end to the epidemic.

“The outbreak of Ebola virus disease in Liberia is over,” the W.H.O. said in a statement read by Dr. Alex Gasasira, the group’s representative to Liberia, in a packed conference room at the emergency command center in Monrovia, the capital.

Just before Dr. Gasasira’s statement, Luke Bawo, an epidemiologist, showed a map depicting all of Liberia in green with the number 42 superimposed on it. This represented that two maximum incubation periods of the virus, a total of 42 days, had passed since the safe burial of the last person confirmed to have had Ebola in the country, fulfilling the official criteria for concluding that human-to-human transmission of the virus has ended.

The room, packed with reporters, workers from Doctors Without Borders and other aid agencies and dignitaries, including the American ambassador to Liberia, Deborah R. Malac, burst into applause, and some people cried, according to health officials who were present.