The present work reports the theoretical considerations of the effects of nontrigonal crystal field on the electronic structure of ferrous ions induced by tetravalent dopants in YIG. It is found that a spin Hamiltonian can well acount for the spectroscopic properties of the ground orbital singlet of the ferrous ion in YIG. A numerical method is worked out to calculate the parameters involved in the theory, namely, the three second‐order and the five fourth‐order zero‐field parameters, and the four components of the Zeeman g‐tensor. A wide range of the microscopic parameters is considered and some representative results are given. The properties of the nearby (I) and far (II) ferrous centers can now be well explained. The centers II are shown to be more anisotropic than the centers I. The dominant second‐order axial parameter is found to be positive and of the value of several inverse cm.