Poly(heptazine imides) hosting cobalt ions as countercations are presented as promising electrocatalysts for the oxygen evolution reaction (OER). A facile mixed‐salt melt‐assisted condensation is developed to prepare such cobalt poly(heptazine imides) (PHI‐Co). The Co ions can be introduced in well‐controlled amounts using this method, and are shown to be atomically dispersed within the imide‐linked heptazine matrix. When applied to electrocatalytic OER, PHI‐Co shows a remarkable activity with an overpotential of 324 mV and Tafel slope of 44 mV dec−1 in 1 m KOH. Poly(heptazine imides) hosting cobalt ions (PHI‐Co) are synthesized by a mixed molten salt method. Due to the abundant, well‐distributed Co ions within the PHI matrix, these materials are promising electrocatalysts for the oxygen evolution reaction (OER) with an overpotential of 324 mV and Tafel slope of 44 mV dec−1 in 1 m KOH.