The room temperature growth and morphology of epitaxial Co films on Cu(100) were studied from the initial nucleation of islands through thicknesses of several monolayers using in situ nanometer resolution ultrahigh Vacuum scanning electron microscopy, Auger electron spectroscopy, and the surface magneto-optic Kerr effect. The films became ferromagnetic at room temperature at similar to 1.7 ML (1 ML=1.53x10(15) atoms/cm(2)). Roughening structures, seen as large inclusions into step bands and terrace pits from which Cu may have migrated, were observed. Minimization of surface energy along step edges is offered as a possible explanation for the observed morphology at the beginning stages of the formation of these structures. A second Co magnetic phase was detected in many films with out-of-plane remanence and a coercivity 5-10 times the in-plane value.