In Baltimore, there was a rapidly growing population of West Indians who had fled the Haitian Revolution, and French who had fled the French Revolution; in a short time, they doubled the total number of Catholics in the United States. DuBourg began ministering to these French-speaking immigrants and holding classes for their children, as well as those of Spanish immigrants. By teaching these classes, DuBourg learned English, and came to be regarded as a polished and effective preacher.