The equiatomic alloy CoGa is almost completely ordered in the B2 ( CsCl ) structure and is paramagnetic. The partial substitution of a 3d transition metal TM for Ga results in series having the general formulae Co 2 Ga 2− x TM x and the magnetic properties and crystallographic states of order of these series have been determined using magnetization, X‐ray, neutron diffraction and resistivity techniques. In some of the series the appearance of a (111) line in the powder diffraction patterns signifies the establishment of double ordering of the L21 type. In the case of TM = Ti this order appears to be established for small values of x. In all the series ferromagnetism is observed beyond a critical concentration and this appears to be related primarily to the electron concentration rather than to any change in ordering which may occur.