The 1866 Atlantic hurricane season was originally one of only four Atlantic hurricane seasons in which every known tropical cyclone attained hurricane status, along with 1852, 1858, and 1884. Initially, there were three known storms during the season, but a re-analysis confirmed the increased activity. There were also two other systems that were included as tropical cyclones at one time, although both were considered to have been other storms already in the database. All tropical activity occurred between the middle of July and the end of October. There may have been additional unconfirmed tropical cyclones during the season. Meteorologist Christopher Landsea estimates that up to six storms were missed from the official database, due to small tropical cyclone size, sparse ship reports, and relatively unpopulated coastlines.