San Nicolás de los Arroyos is a city in the province of Buenos Aires, Argentina, on the western shore of the Paraná River, 61 km (38 mi) from Rosario. It has about 133,000 inhabitants. It is the administrative seat of the partido of the same name. It is sometimes called Ciudad de María due to a series of Marian apparitions that led to the erection of the Sanctuary in honor of Our Lady of the Rosary of San Nicolás that began during the 1980s and were approved by Bishop Cardelli of the diocese as "worthy of belief" in 2016.

Buenos Aires, officially the Buenos Aires Province, is the largest and most populous Argentine province. It takes its name from the city of Buenos Aires, the capital of the country, which used to be part of the province and the province's capital until it was federalized in 1880. Since then, in spite of bearing the same name, the province does not include Buenos Aires city, though it does include all other parts of the Greater Buenos Aires metropolitan area. The capital of the province is the city of La Plata, founded in 1882.