The cation ratio, crystal structure, and ferroelectric properties of TbMnO₃ films on (010) oriented YAlO₃ substrates grown by pulsed laser deposition were investigated. We found that the cation ratio is altered by the background gas pressure, and that stoichiometric films have larger critical thicknesses than Tb-rich films. The ferroelectric order was severely disturbed in Tb-rich films showing a lower transition temperature and a smaller polarization. In addition, frequency dispersion was observed in the dielectric response of relaxed stoichiometric TbMnO₃ films, which may be introduced by defects due to strain relaxation.