The dynamic susceptibility study of photoinduced magnetism in a molecule-based magnet, K1-2xCo1+x[Fe(CN)(6)];yH(2)O (0.2</=x</=0.4,y approximately 5), is reported. Upon excitation with visible light the material has substantial changes in linear and nonlinear ac susceptibility and dc magnetization. The results demonstrate cooperative freezing of magnetic moments and absence of true long-range magnetic order. The ground and photoexcited states are described within a cluster glass model, with photoinduced increase in spin concentration leading to a shift of the dynamics to longer length and time scales and higher temperatures.