Jamaica is the largest source of English-speaking Caribbean emigrants.
As of now, there are 3 million persons living in Jamaica. The domestic population has experienced a declining fertility rate, going below the 2.1 births per woman replacement rate in the early 2010s.
Among living Jamaicans, 1.2 million live outside the country today, inferring that upwards of 29% of Jamaicans live outside Jamaica (1.2 + 3 = 4.2 total). Of the 1.2 million, two thirds, or about 800,000, live in the U.S. They comprise by far the largest share of English-speaking Caribbean immigrants in the U.S.
There are large communities the United States, the UK, and Canada of Jamaicans born in Jamaica and offspring of earlier immigrants. The percentage of residents who are of Jamaican heritage: London 4%; Toronto 3.4%.
From here, here and here.