When did the Catholic Church first make an official statement on the Millenarianism?
The only “official” statement that I can find comes from a Decree of the Holy Office, July 21, 1944.
The Catechism of the Catholic Church states:
The Antichrist’s deception already begins to take shape in the world every time the claim is made to realize within history that messianic hope which can only be realized beyond history through the eschatological judgment. The Church has rejected even modified forms of this falsification of the kingdom to come under the name of millenarianism (577), especially the “intrinsically perverse” political form of a secular messianism. (578) — n. 676
I deliberately left in the footnote references above because they are crucial in helping us understand what is meant by “millenarianism”, and secondly, “secular messianism” in the Catechism.
…the system of mitigated Millenarianism, which teaches, for example, that Christ the Lord before the final judgment, whether or not preceded by the resurrection of the many just, will come visibly to rule over this world. The answer is: The system of mitigated Millenarianism cannot be taught safely. — DS 2296/3839, Decree of the Holy Office, July 21, 1944
Millenarianism — What it is, and is not
It is a well known fact that after St. Augustine championed against millennialism as is understood by modernists. In fact, St. Augustine held to the conviction that there will be no millennium.
Millennialism in the Early Church was understood differently than in modern times.
St. Augustine was for a time, as he himself testifies (City of God XX.7), a pronounced champion of millenarianism; but he places the millennium after the universal resurrection and regards it in a more spiritual light (Sermo, CCLIX). When, however, he accepted the doctrine of only one universal resurrection and a final judgment immediately following, he could no longer cling to the principal tenet of early chiliasm. St. Augustine finally held to the conviction that there will be no millennium. - Millennium and Millenarianism
From the time of St. Augustine Millennialism died as a theological belief until the Reformation. The Middle Ages, was never tainted with millenarianism or Premillennialism.
The Middle Ages were never tainted with millenarianism; it was foreign both to the theology of that period and to the religious ideas of the people...Hence the millennium proper is unknown to them. The Protestantism of the sixteenth century ushered in a new epoch of millenarian doctrines. Protestant fanatics of the earlier years, particularly the Anabaptists, believed in a new, golden age under the sceptre of Christ, after the overthrow of the papacy and secular empires. In 1534 the Anabaptists set up in Münster (Westphalia) the new Kingdom of Zion, which advocated sharing property and women in common, as a prelude to the new kingdom of Christ. Their excesses were opposed and their millenarianism disowned by both the Augsberg (art. 17) and the Helvetian Confession (ch. 11), so that it found no admission into the Lutheran and Reformed theologies. Nevertheless, the seventeenth and eighteenth centuries produced new apocalyptic fanatics and mystics who expected the millennium in one form or another: in Germany, the Bohemian and Moravian Brethren (Comenius); in France, Pierre Jurien (L'Accomplissement des Propheties, 1686); in England at the time of Cromwell, the Independents and Jane Leade. A new phase in the development of millenarian views among the Protestants commenced with Pietism. One of the chief champions of the millennium in Germany was I.A. Bengel and his disciple Crusius, who were afterwards joined by Rothe, Volch, Thiersch, Lange and others. Protestants from Wurtemberg emigrated to Palestine (Temple Communities) in order to be closer to Christ at His second advent. Certain fantastical sects of England and North America, such as the Irvingites, Mormons, Adventists, adopted both apocalyptic and millenarian views, expecting the return of Christ and the establishment of His kingdom at an early date. Some Catholic theologians of the nineteenth century championed a moderate, modified millenarianism, especially in connection with their explanations of the Apocalypse; as Pagani (The End of the World, 1856), Schneider (Die chiliastische Doktrin, 1859), Rohling (Erklärung der Apokalypse des hl. Iohannes, 1895; Auf nach Sion, 1901), Rougeyron Chabauty (Avenir de l'Église catholique selon le Plan Divin, 1890). - Millennium and Millenarianism
Thus we can see that it was not until recent times that the Church has had to address this subject matter and remains of little interest in Catholic circles even today.
The following articles may be of interest to some: