  We report the effect of 3 MeV proton irradiation on the suppression of the
critical temperature $T_{c}$ in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ single
crystals at under-, optimal-, and over-doping levels. We find that $T_{c}$
decreases and residual resistivity increases monotonically with increasing
dose. We also find no upturn in low-temperature resistivity in contrast with
the $\yen alpha$-particle irradiated NdFeAs(O,F), which suggests that defects
induced by the proton irradiation behave as nonmagnetic scattering centers. The
critical scattering rate for all samples estimated by three different ways is
much higher than that expected in $s_{\yen pm}$-pairing scenario based on
inter-band scattering due to antiferro-magnetic spin fluctuation.
