Priority mapping areas of the Long Island Sound Seafloor Habitat Mapping Initiative (LISSHMI; https://longislandsoundstudy.net/research-monitoring/seafloor-mapping/). Data presented show completion progress of benthic mapping and seafloor characterization for elements of different project phases within these areas. LISSHMI is administered by the Long Island Sound Cable Fund Steering Committee, comprised of representatives of the EPA Region 1 and Region 2 offices, the Connecticut Department of Energy and Environmental Protection, the New York State Department of Environmental Conservation, and Connecticut and New York Sea Grant Programs, and managed by the Connecticut Department of Energy & Environmental Protection Land & Water Resources Division. Project phases for seafloor mapping and habitat characterization have been funded under the Long Island Sound Research and Restoration Fund, EPA-Long Island Sound Study supplemental budget program funds, and the NOAA Office of Coast Survey Rear Admiral Richard T. Brennan Ocean Mapping Matching Fund Program (for Phase VA).