When and who declared the Immaculate Conception the patroness of the United States of America?
- “Patronages of the Immaculate Conception: America (United States).” In Wikipedia, December 7, 2022:
On 13 May 1846, the United States bishops unanimously chose “the Virgin Mary, conceived without Sin”, as patroness of the country, a decision approved by Pope Pius IX on February 7 of the following year and published in a decree of 2 July 1847.1
On 10 April 1848, a voting process and discussion was made on the regularisation of the rubrics for the Feast of the Immaculate Conception to be celebrated in that country. By 1849, this decree was published at the 7th Provincial Council of Baltimore.2 The decrees were signed and witnessed by Cardinal Giacomo Filippo Fransoni.3
On 8 July 1914, Pope Pius X sent an apostolic letter to Archbishop of Baltimore, Cardinal James Gibbons approving the patronage of the Immaculate Conception for the new construction site of the National Shrine of the Immaculate Conception.
On 10 April 1919, Pope Benedict XV reiterated this patronage and stated that he had ordered a mosaic of Our Lady of the Immaculate Conception to be made in the Vatican Mosaic Studio for the shrine's high altar.4
In 1923, Pope Pius XI chose a mosaic version of Bartolomé Esteban Murillo's La Purísima Inmaculada Concepción for installation at the shrine, the image is a mosaic rendition of the venerated Immaculate Conception enshrined at the Royal Palace of Aranjuez.5 now installed in the largest Roman Catholic church in the United States of America.
- Archdiocese of Baltimore (1851). Concilia provincialia, Baltimori habita ab anno 1829 usque ad annum 1849. apud Joannem Murphy et socium. p. 255-256. Sanctis Congregationis Generalis de Propaganda Fide Quo Deipara Virgo, Sine Labe Originali Concepta, Septentrionalis Americae Foederatae Provincialum Patrona Instituitur
- "Land Of Mary Immaculate". Ewtn.com. 1996. Archived from the original on 11 March 2019. Retrieved 27 February 2014.
- Fanning, William (1907). "Provincial Councils of Baltimore". The Catholic Encyclopedia. Vol. 2. New York: Robert Appleton Company. Retrieved 16 September 2019 – via NewAdvent.org.
- Benedictus PP. XV (10 April 1919). "Epistola Communes litteras, al Cardinale Giacomo Gibbons e al Cardinale Guglielmo O'Connel, di Benedetto XV, 10 aprile 1919". Vatican.va. Libreria Editrice Vaticana. Archived from the original on 3 March 2013. Retrieved 27 February 2014.
- Tucker, Gregory W. (1 January 2000). America's church: the Basilica of the National Shrine of the Immaculate Conception. Our Sunday Visitor Publishing. p. 22, 33-34. ISBN 9780879737009.
I believe that, owing the Shrine being a minor-Basilla (so declared by Pope John Paul II in 1990) and because is lies within the Archdiocese of Baltimore, which is where the primate of the United States, Our Lady (of) the Immaculate Conception is the Patroness of the United States (whereas Our Lady of Guadalupe is the Patroness of the Americas in general).
Bishop Thomas J. Shahan was the bishop who wanted to get the shrine started, back in the 1910's, he went to Pope Pius X to get his approval and the pope personally donated $400 for his project back in 1913 - so perhaps that was the first/highest declaration of what would inevitably become the patronage of the USA.
-- source: Sept 23 reading in American Catholic Daily Reader by Brian Burch and Emily Stimpson Chapman.