Facile synthesis of photocatalysts with highly dispersed metal centers is a high-priority target yet still a significant challenge. In this work, a series of Co-C₃N₄ photocatalysts with different Co contents atomically dispersed on g-C₃N₄ have been prepared via one-step thermal treatment of cobalt-based metal-organic frameworks (MOFs) and urea in the air. Thanks to the highly dispersed and rich exposed Co sites, as well as good charge separation efficiency and abundant mesopores, the optimal 25-Co-C₃N₄, in the absence of noble metal catalysts/sensitizers, exhibits excellent performance for photocatalytic CO₂ reduction to CO under visible light irradiation, with a high CO evolution rate of 394.4 μmol·g^–1·h^–1, over 80 times higher than that of pure g-C₃N₄ (4.9 μmol·g^–1·h^–1). In addition, by this facile synthesis strategy, the atomically dispersed Fe and Mn anchoring on g-C₃N₄ (Fe-C₃N₄ and Mn-C₃N₄) have been also obtained, indicating the reliability and universality of this strategy in synthesizing photocatalysts with highly dispersed metal centers. This work paves a new way to develop cost-effective photocatalysts for photocatalytic CO₂ reduction.