[en] We report a comprehensive study of the tridimensional nature and orbital characters of the low-energy electronic structure in KCo₂Se₂, using polarization- and photon energy-dependent angle-resolved photoemission spectroscopy. We observed one electron-like Fermi surface (FS) at the Brillouin zone (BZ) center, four electron-like FSs centered at the BZ corner, and one hole-like FS at the BZ boundary. The FSs show weak dispersion along the k_z direction, indicating the near-two-dimensional nature of FSs in KCo₂Se₂. In combination with the local-density approximation calculations, we determined the orbital characters of the low-energy electronic bands, which are mainly derived from the Co 3d orbital, mixed with part of the Se 4p states. The $d_{x^2-<!--\; ???\; -->y^2}$ orbital gives a significant contribution to the band crossing the Fermi level. A band renormalization of about 1.6 is needed to capture the essential dispersive features, which suggests that electronic correlations are much weaker than that in K_yFe_2−xSe₂. (paper)