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The understanding of excited state dynamics in iron-based superconductors is the subject of great interest in theoretical and experimental condensed matter physics. Here we report on time-domain studies of light-induced quasiparticle dynamics in Co-doped BaFe₂As₂ superconducting epitaxial thin films at different excitation regimes. The evolution of transient optical signal in superconducting and non-superconducting states reveals several regions with noticeably different electron-phonon relaxation. The most distinct dynamics associated with multi-stage quasiparticle relaxation rise up on a sub-30 ps time scale. The sub-500 fs process is associated with the instantaneous formation of the nonequilibrium state of quasiparticles. It is followed by the energy exchange between this photoexcited state and lattice with electron thermalization within 3 ps. The characteristic time of this process grows with excitation and is associated with the evolution of quasiparticles and, possibly, hidden phases. New mechanisms seem to underpin the photoinduced relaxation dynamics of Co-doped BaFe₂As₂ in low- and high-excitation regimes.