Cedar Beach is located on a peninsula that stretches for over a mile westward, with the Long Island Sound to its north and Mount Sinai Harbor to its south.

Nearer to Cedar Beach's western end is a boat launch ramp and marina, with the Mount Sinai Yacht Club located on the peninsula.

Prior in the mid-19th century, the mouth of Mount Sinai Harbor was on at its eastern side, with the peninsula on which Cedar Beach now sits being accessible from Port Jefferson.

During the Revolutionary War, Cedar Beach was the landing site of Major Benjamin Tallmadge and his detachment of Continental Army dragoons during a successful raid on British forces.

Cedar Beach has been a popular recreational area since the expansion of the Long Island Rail Road to neighboring Port Jefferson in 1873 (and temporarily to Mount Sinai from 1895-1939).