He served as sheriff of Westchester County from 1769 to 1776 and as an officer in the militia. Because of his loyalist sympathies, he was forced to leave the area and went to
New York City, where his uncle,
Oliver De Lancey, raised a loyalist military unit known as
De Lancey's Brigade. James commanded his own, irregular
guerrilla unit, known as '''De Lancey's Raiders
, De Lancey's Refugees
, Westchester Refugees,
and the "Cowboys
" or "Cow-boys'''." His much-feared partisans harassed the enemy near New York City and procured supplies for the British army by conducting
cattle raids. James acquired the sobriquet “Outlaw of the Bronx” (De Lancey had his headquarters near the
Bronx River.) Forces under James De Lancey ambushed and killed Colonel
Christopher Greene and Major Ebenezer Flagg of the
Rhode Island Regiment of the
Continental Army at the
Battle of Pine's Bridge on May 14, 1781. According to historian Otto Hufeland, "it was one of the few expeditions in which Colonel Delancey himself took part." The Cowboys often operated under the broader umbrella of the De Lancey name and worked closely with his uncle's De Lancey's Brigade.
Nova Scotia . Around the start of 1783, following the Patriot victory in the American Revolution, he moved to Nova Scotia, settling at
Round Hill in
Annapolis County. De Lancey was elected to the provincial assembly after his brother
Stephen accepted an office in the Bahamas. James took his seat representing
Annapolis Township from Feb. 26, 1790, until he was named to the province's
Council in 1794 by
Governor Wentworth. ==Personal life==