Africans imported into New York found a ready market. The ownership of slaves was widespread in early New York: of the forty‑eight heads of household in Flushing in 1675, ten (20.8 percent) held slaves. In 1683 five (13.2 percent) of the thirty‑eight householders in Flatlands owned slaves. In 1686 Southold's 114 families included 12 (10.5 percent) who owned slaves. In New Utrecht in 1693 ten of the forty‑three household heads (23.3 percent) were slaveowners. Kings County (predominantly Dutch) had an even larger black population: 40.7 percent of white households contained slaves (129 out of 317 households) in 1698.
. . . .
In the town of Brooklyn 33.7 percent of households held slaves, 36.2 percent in Bushwick, 51.4 percent in Flatlands, 32.4 percent in Gravesend, 48.5 percent in Flatbush, and 46.3 percent in New Utrecht. Large proportions of the white population continued to use slave labor in New Utrecht: 50 percent in 1716 and 47.4 percent in 1717. The need for farm labor was great in Kings County, for in addition to the 295 slaves in the county in 1698 there were also 48 apprentices.
. . . .
In the 1830s blacks began to settle on lands in the semi‑rural outskirts of Brooklyn (present‑day Bedford Stuyvesant) in Kings County. Known as Weeksville‑Carrsville, the section contained forty property‑owning black families in 1841.57 Large settlements of impoverished former slaves lived in the towns of Jamaica and Flushing in Queens County.
Another interesting site is http://fisher.lib.virginia.edu/collections/stats/histcensus/php/county.php, which has a database of census data. In its breakdown of the population county by county in New York in 1840, there were 2,843 "free colored persons" in Kings county out of a total population of 47,613. It reports that the total number of slaves in the state that year was 4, with 3 of them in Kings county.