Brooklyn (NYC borough) is 3 times larger than San Marino.
Area: 61 km2 World Factbook
Population: 32,742 (July 2014) World Factbook
San Marino, officially the Republic of San Marino and also known as the Most Serene Republic of San Marino, is an enclaved microstate surrounded by Italy, situated on the Italian Peninsula on the north-eastern side of the Apennine Mountains. Wikipedia
Area: 180 km2 calculated
Brooklyn is the most populous of New York City's five boroughs, with about 2.6 million people, as well as the second-largest in area. Wikipedia