The ternary solid solution relating CoSb and Fe1+Sb has been synthesized and the Fe spin dilution effects on the magnetic properties has been investigated. The Fe magnetic moments are localized despite the fact that the metallic character increases with the Fe concentration. The covalent bonding along the c direction that is responsible for the metallic character is also responsible for a smaller magnetic moment on Fe sites, which depends on the Fe concentration. On the Fe-rich side, the antiferromagnetic (AF) ordering is observed down to a Fe concentration that is comparable to the site percolation threshold for the basal plane. At lower temperatures, re-entrant spin-glass phases are observed, which become spin-glass phases below the percolation threshold for AF ordering. The dynamic scaling shows the same behavior as that of the conventional spin glasses in which the Ising anisotropy is small.