Although migration from Puerto Rico to the US mainland is not an entirely new phenomenon—several Puerto Rican merchants were living in New York City as early as 1830—there were no more than 70,000 islanders in the US in 1940. Mass migration, spurred by the booming postwar job market in the US, began in 1947. The out-migration was particularly large from 1951 through 1959, when the net outflow of migrants from the island averaged more than 47,000 a year. According to the 2000 census, 3,406,178 ethnic Puerto Ricans were living in the 50 states; at least 32 cities had Puerto Rican communities of 5,000 or more. Puerto Ricans are found in significant numbers not only in New York State but also in New Jersey, Illinois, Pennsylvania, California, Florida. Connecticut, and Massachusetts. Indeed, 58% of ethnic Puerto Ricans living in the 50 states were concentrated in the Northeast in 2002.
During the 1970s, in part because of the economic decline of many US urban centers, the migration trend slowed; official estimates show that the net flow of migrants from the island totaled only 65,900. But with the Puerto Rican economy worsening in the early 1980s, the net migration from early 1980 to mid-1983 was about 90,000. From 1990 to 1992, there was a net loss from migration of about 40,000.
One striking aspect of the US-Puerto Rico migration pattern is its fluidity. As US citizens, Puerto Ricans can move freely between the island and the mainland. Even in 1953, when the heaviest net outflow was recorded—74,603—fully 230,307 persons emigrated from the US mainland to Puerto Rico, as 304,910 Puerto Ricans were migrating the other way. In 2000, 242,973 people living on the US mainland said that they had lived in Puerto Rico in 1995, while 112,788 people living in the commonwealth in 2000 said that they had lived on the mainland in 1995. This extreme mobility, though sensitive to the job market, would not be possible were it not for the increased income available to Puerto Ricans on both the island and the US mainland, and the fact that Puerto Ricans who come to the continental US generally preserve their ties of family and friendship with those in the commonwealth, thus finding it easy to return, whether for a short stay at Christmastime or for a new job on the island.