Suffolk County is a county located in the U.S. state of New York. As of 2000, the population was 1,419,369. It was named for the county of Suffolk in England, from which its earliest settlers came. The county seat is Riverhead, though many county offices are in Hauppauge on the west side of the county where most of the population lives. There are also offices in Smithtown, for the legislature, and Yaphank.

Suffolk and Nassau counties are generally referred to as Long Island by area residents (as distinct from Brooklyn and Queens, both physically on Long Island but part of New York City). Suffolk County is the easternmost county in New York State and the New York Metropolitan Area.