The rotational level populations of CO molecules were measured in CO(<10%) + Ar free jets by electron beam fluorescence (in a stationary jet) and resonantly enhanced multiphoton ionization (in a pulsed jet). The measured evolution of the nonequilibrium rotational energy was used to derive the rotational relaxation cross sections in the temperature range from 7 to 150 K. Using the pressure-broadened linewidth data the state-to-state rotational relaxation rate coefficients were found using the most popular fitting law forms: The modified exponential gap, the statistical polynomial-exponential gap, and the energy corrected sudden approximation. The fitted rates were compared with the experimental and theoretical data presently available in the literature. They were checked also by consideration of the rotational kinetics in free jets and by comparison between the computed and experimental rotational level populations both in near and far regions of a flow.