Fr. Ilarion was born as Ivan Fomich Prikhodko () in the village of Alenovka in the Unechsky District, Bryansk Oblast. His parents Foma and Iuliana gave him and his two siblings a pious upbringing. The family worked the land until the Soviets dispossessed them in the drive to collectivize farming. The Germans took whatever was left after they occupied the territory during the Second World War. Young Ivan joined the army in 1943 and covertly practiced his faith. The horrors of war and a severe combat injury he suffered shook him to the core. In the hospital, after meeting two nuns of the Catacomb Church, he decided that he himself would become a monk. After the war, his mother blessed his new path; his father was deeply upset, but did not prevent Ivan from entering the monastery.