Both theoretical and experimental evidence have recently indicated that magnetic circular dichroism in Si doped YIG is a manifestation of the same ’’impurity centers’’ responsible for the photoinduced effects in this material. In this paper we report measurements of magnetic circular dichroism in (011) plates of Si and Sn doped crystals at 4.2°K. Magnetic circular dichroism was measured in the wavelength range 1.1−1.6μm. Results for the two different dopants are compared and discussed. It appears that magnetic circular dichroism occurs both for Si which prefers tetrahedral sites and for Sn which prefers octahedral sites. However, the detailed dependence on wavelength is markedly different for the two dopants. To our knowledge this is the first demonstration that the properties of the Fe++ ion depend on the identity of the compensating ion.