Hawthorne is an unincorporated hamlet and census-designated place (CDP) located in the town of Mount Pleasant in Westchester County, New York. The population was 5,083 at the 2000 census.
The village was originally known as Hammond's Mills, and was part of Frederick Philipse's estate Philipsburgh. On September 23, 1783 Major John André stopped here on his way to New York to ask directions after meeting with Benedict Arnold.
After the Revolutionary War, the name of the village changed to Unionville. The hamlet's population consisted mostly of farmers. The Reformed Church of Unionville (Hawthorne Reformed Church) was built here in 1818. In 1832, a one-room school house was built. In 1847, a railroad station was established on New York Central's Harlem Division, with the name Unionville. A post office was also established on February 10, 1851, and was designated Neperan after the Indian name for the Saw Mill River.