A Hirayama family of asteroids in the outer region of the main asteroid belt at a mean distance of 3.02 au from the Sun. Most Eos family members have surface properties roughly intermediate between S and C types, tending towards the S type especially in albedo. The family is named after (221) Eos, an S-type asteroid, diameter 104 km, discovered in 1882 by the Austrian astronomer Johann Palisa (1848–1925). Its orbit has a semimajor axis of 3.01 au, period 5.22 years, perihelion 2.70 au, aphelion 3.32 au, and inclination 10°.9.