there were churches in Sumer and Ur at least 4ooo BC.
If you mean the New Testament church, the answer is Jerusalem.
If you mean "First Christian Church", then it's in Antioch, Turkey where Paul and his Gentile followers were first called Christians.
Acts 11:26 And when he had found him, he brought him unto Antioch. And it came to pass, that a whole year they assembled themselves with the church, and taught much people. And the disciples were called Christians first in Antioch.