From the Catholic Encyclopedia:
Church troubles, Trusteeism in New York, and Nationalism in Philadelphia, at this time decided the priests of Maryland (March, 1788) to petition Rome for a bishop for the United States. Cardinal Antonelli replied, allowing the priests on the mission to select the city and, for this case only, to name the candidate for presentation to the pope. Twenty-four of the twenty-five other priests in the meeting voted for Father Carroll. Accordingly on 6 November, 1789, Pope Pius VI appointed him bishop. His consecration took place in Mr. Weld’s chapel at Lulworth Castle, England, 15 August, 1790, at the hands of the Rt. Rev. Charles Walmesley, Senior Vicar Apostolic of England. Bishop Carroll returned to Baltimore in triumph, 7 December, when he preached an appropriate and touching sermon in St. Peter’s church. Troubles in Boston required him soon to go thither, where he removed much prejudice.
[http://www.newadvent.org/cathen/03381b.htm]
