209 Dido is a main-belt asteroid with a diameter of 179 km. It was discovered by C. H. F. Peters on October 22, 1879, in Clinton, New York and was named after the mythical Carthaginian queen Dido. This asteroid is orbiting the Sun at a distance of 3.15 AU with an eccentricity (ovalness) of 0.058 and a period of 2041.8 days. The orbital plane is tilted at an angle of 7.2° to the plane of the ecliptic. 209 Dido is classified as a C-type asteroid and is probably composed of carbonaceous materials. Like many asteroids of its type, it has an extremely low albedo. Photometric observations at the Palmer Divide Observatory during 2005 showed a rotation period of 5.737 hours with a brightness variation of 0.17 in magnitude. The pole orientation in ecliptic coordinates, as determined from multiple light curve studies, is (βp, λp) = (120 °, 66 °). 209 Dido has been observed to occult 4 stars between 2005 and 2023.