Long Island is located in the southeastern part of New York, Percy Jackson's home state, aside the Atlantic Ocean. To the north is Long Island Sound. Long Island is connected to New York City by various bridges and the Long Island Rail Road. Camp Half-Blood is said to be located here, at 3.141 Farm Road, Montauk. Sally Jackson also rents a small beach house on the shoreline where she sometimes takes Percy during the summer. Long Island is also where Sally met Poseidon. It is also briefly mentioned in the Kane Chronicles, where a strange magical frequency was emitting from that area.
Long Island is home to Camp Half-Blood and is a location in every single book.
Long Island appeared briefly in The Lost Hero, and was the main setting for The Son of Sobek. Long Island also appears in the windows of the Argo II's mess hall and the seven go to Camp Half-Blood to help the demigods defeat Gaia and the monsters. The seven return to Long Island after defeating the giants.
Brooklyn House, the headquarters for the twenty-first nome is located on the western most section of the island.
Long Island, namely Camp Half-Blood, is the primary setting of the story.