In situ cantilever curvature is used to quantify the growth stress in Co thin films, electrodeposited from an electrolyte consisting of 0.5 mol/L Na2SO4, 0.5 mol/L H3BO3, and 0.1 mol/L CoSO4 center dot 7 H2O. The average biaxial steady-state stress is measured as a function of the deposition potential and is examined as a function of growth rate. Stresses as low as + 85 MPa (tensile) are obtained at small growth rate, increasing to a limiting value of 800 MPa as the growth rate is increased. The data is fit to a kinetic model that appears in the literature and treats the stress as a dynamic competition between coalescence-induced tensile stress and compressive stress due to insertion of atoms into the grain boundary. Kinetic parameters for Co indicate that stress development is dominated by nuclei coalescence and that ad-atom insertion into the grain boundary contributes to the overall stress only at very low growth rates. (C) The Author(s) 2019. Published by ECS.