Named, according to Brooklyn by Name, after a developer called James Halsey.
Forgotten New York, citing the reference book Brooklyn by Name, says Halsey Street honours ‘a colonial-era developer James Halsey’; nothing more is known about him from the sources found. The street runs from Bedford–Stuyvesant into Bushwick; an older Margaretta (or Margareta) Street became part of it, and in 1889 it was cut through to the ball grounds beyond the county line.