Sullivan's Island is located about 3.5 miles northeast of Charleston.  The Island is about 2 1/2 miles long and about 1/2 mile wide at its widest point.  The total area within the Town limits is about 2,000 acres of high ground, with an additional 1,100 acres in marshland.

Sullivan's Island is located in the outer coastal plain, a portion of the Atlantic coastal plain made up of barrier islands unique to the coastal areas of the southeastern United States.  The area is relatively flat, except for large man-made mounds built by the US Army when stationed on the Island.  The Town's elevation ranges from seal-level to about fourteen (14') feet above sea level, with a wide range between high and low tides.

The Federal Emergency Management Agency (FEMA) has mapped Sullivan's Island identifying various areas of flood hazards.  Areas located in VE zones are subject to inundation by the one (1%) percent flood level with additional hazards due to velocity (wave action).  Areas located in AE zones are subject to inundation by the one (1%) percent flood level determined in a Flood Insurance Study.  Base flood elevations are shown within these zones and mandatory flood insurance purchase requirements apply.

Oceanfront property is located in a VE flood zone with the flood elevation ranging from 15 to 23 feet, depending on the location of the property.  The eastern end of the Island is located in the higher VE flood zone with flood elevation ranging from 19 to 23 feet.  A portion of the commercial properties located between Station 22 and 22 1/2 are located in the VE elevation 16 flood zone.  The middle and marsh sides of the Island are generally located within an AE flood zone with the flood elevation ranging from 13 to 15 feet.