High quality single-crystal fcc-Co(x)(Mg(y)Zn(1-y))(1-x)O(1-v) epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Co(x)(Mg(y)Zn(1-y))(1-x)O(1-v) films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed with both controllable magnetic properties and tunable band-gap, Co(x)(Mg(y)Zn(1-y))(1-x)O(1-v) films may have promising applications in future spintronics.