What was the first church that was built?

We are unlikely ever to know where the first church was, but archaeologists believe they have found the world's oldest remaining church, dating back to between 33 and 70 CE. If tests confirm this, it would make it the earliest known place of Christian worship by about 200 years.

The head of the Rihab Centre for Archaeological Studies, Abdul Qader al-Husan, says a very early underground church has been found beneath the ancient St Georgeous Church, which itself dates back to AD230, in Rihab, northern Jordan, near the Syrian border.

Catholic Answer

The word "church" is used in many different ways in contemporary society, depending upon your background and education. The Catholic Church has always used the word "Church" to describe the faithful who believe in Jesus Christ and are led by His appointed shepherds: His Vicar, the Pope, and the Bishops and Priests under him. Thus for a Christian, the Church was built upon St. Peter - see St. Matthew 16:17-19 for Our Lord's establishment of His Church.

When Our Blessed Lord established His Church, He made it plain that it would be One and Holy. He put St. Peter as His first Vicar (St. Matthew 16:17-19) after the pattern of the Davidic Kingdom which He was re-establishing. This whole episode in St. Matthew is based on the imagery of the Keys from the Davidic Kingdom in Isaiah, see Isaiah 22:15-25). As St. Paul points out the Church is Our Blessed Lord's Mystical Body (Colossians 1:18, 2:18-20, 1 Cor 12:12-31; Eph. 1:22-23; 3:19; 4:13). St. Paul doesn't use the word, Mystical, that was a later explanation by the Church as this is a mystery. The point is He only has ONE Body and it is the Church, so the Church remains, as recited in the Nicene Creed: One, Holy, Catholic, and Apostolic. It WAS the early Church, it was the medieval Church, and it is the modern Church, and it will remain the Church until the end of the world, we have the guarantee of Our Blessed Lord, and the Holy Ghost on this.

from Modern Catholic Dictionary by John A. Hardon, S.J. Doubleday & Co., Inc. Garden City, NY 1980
Church. The faithful of the whole world. This broad definition can be understood in various senses all derived from the Scriptures, notably as the community of believers, the kingdom of God, and the Mystical Body of Christ. As the community of believers, the Church is the assembly (ekklesia) of all who believe in Jesus Christ; or the fellowship (koinoia) of all who are bound together by their common love for the Savior. As the kingdom (basileia), it is the fulfillment of the ancient prophecies about the reign of the Messiah. And as the Mystical Body it is the communion of all those made holy by the grace of Christ. He is their invisible head and they are his visible members. These include the faithful on earth, those in purgatory who are not yet fully purified, and the saints in heaven.

Since the Council of Trent, the Catholic Church has been defined as the union of human beings who are united by the profession of the same Christian faith, and by participation of and in the same sacraments under the direction of their lawful pastors, especially of the one representative of Christ on earth, the Bishop of Rome. Each element in this definition is meant to exclude all others from actual and vital membership in the Catholic Church, namely apostates and heretics who do not profess the same Christian faith, non-Christians who do not receive the same sacraments, and schismatics who are not submissive to the Church's lawful pastors under the Bishop of Rome.

At the Second Vatican Council this concept of the Church was recognized as the objective reality that identifies the fullness of the Roman Catholic Church. But it was qualified subjectively so as to somehow include all who are baptized and profess their faith in Jesus Christ. They are the People of God, whom he has chosen to be his own and on whom he bestows the special graces of his providence. (Etym. Greek kyriakon, church; from kyriakos, belong to the Lord.)