Holtsville, New York

Holtsville, New York
The Holtsville Post Office in 2018.
U.S. Census map of Holtsville
Holtsville, New York
Location within the state of New York
Holtsville, New York
Holtsville, New York (New York)
Coordinates: 40°48′48″N 73°2′50″W / 40.81333°N 73.04722°W / 40.81333; -73.04722
Country United States
State New York
CountySuffolk
TownsBrookhaven
Islip
Area
 • Total
7.11 sq mi (18.41 km2)
 • Land7.11 sq mi (18.41 km2)
 • Water0 sq mi (0.00 km2)
Elevation
105 ft (32 m)
Population
 (2020)
 • Total
18,937
 • Density2,663.9/sq mi (1,028.53/km2)
Time zoneUTC−05:00 (Eastern Time Zone)
 • Summer (DST)UTC−04:00
ZIP Codes
00501, 00544, 11742
Area codes631, 934
FIPS code36-35254
GNIS feature ID0953030

Holtsville is a hamlet and census-designated place (CDP) in Suffolk County, on Long Island, in New York, United States. As of the 2020 census, Holtsville had a population of 18,937.

The hamlet is mainly in the Town of Brookhaven, while the southwestern portion is in the Town of Islip. An IRS Processing Center is located in Holtsville, along with NYPA's Richard M. Flynn Power Plant.