A list of the rarest blood types is maintained online at KnowYourBlood.com. As of 2015, information detailing rare blood types can also be found on the websites of the American Red Cross and New Health Guide.
AB-negative is the rarest blood type in the United States, belonging to less than one percent of the population. B-negative is the next rarest blood type with approximately 1.5 to 1.7 percent of people being born with it. AB-positive is next, followed by A-negative. O-positive blood is the most common blood type in the United States and is found in close to 40 percent of the population.