|The other Petworth|
In 1803, Colonel John Tayloe, one of the wealthiest men in America, bought 100 acres of land north of Rock Creek Church Road. He named in Petworth, after a famous mansion in England. Tayloe bred racehorses on the land, among other things.
In 1887, B.H. Warner and Myron M. Parker bought the land from Tayloe's heirs, and after combining it with some other land to form a 387 acre plot, the area was subdivided for the neighborhood we know today.
The DCist post linked above has more about the neighborhood's history into the 1890s. Always love this kind of thing.