ReaxFF provides a method to describe bond-breaking and bond-forming events that can be applied to large-scale molecular dynamics simulations. This article describes the development of a ReaxFF potential for cobalt. This potential is transferable to a wide variety of cobalt systems, including various crystal structures, surfaces, clusters, and defects. The potential parameters were obtained from an extensive set of ab initio calculations. We have tested these parameters against additional DFT calculations not included in the fitting data set and found that ReaxFF provides similar or superior agreement with the DFT results compared to accepted embedded atom method descriptions for Co. We validated this potential by performing large-scale molecular dynamics simulations to predict the melting point, diffusion coefficients for the liquid as a function of temperature, and vacancy-mediated diffusion coefficients in the solid as a function of temperature and vacancy concentration. Results are compared with other theoretical methods and experiments where available. Since the ReaxFF method allows straightforward extensions to alloys and heterogeneous materials, including first-row elements, the ReaxFF parameters described here provide a foundation for the simulation of a wide range of Co-containing materials.