Eko's church was a structure on the Island near the beach camp, which Eko and Charlie began to build, until Eko found a new purpose in pushing the button. Following Eko's move to the Swan, Charlie attempted to continue work, but found it difficult and got frustrated with Eko's abandonment of the project. The church was located near the survivors' graveyard.
Eko was building the church for Yemi after he killed three men inside Yemi's church in Nigeria. As Eko left Nigeria for London, Amina told him that, because of his actions, he owed Yemi a new church. ("The Cost of Living")
Charlie has difficulty trying to build the church by himself. ("Three Minutes")