Developing highly competent and low-cost earth-plentiful metal-based oxygen evolution reaction (OER) electrocatalysts is critical for future electrochemical conversion technologies and renewable energy systems. Herein, two cobalt-based metal–organic frameworks (Co-MOFs), [Co₆(btc)₂(DMF)₆(HCOO)₆] (2D, MOF 1) and [Co₃(CHOO)₉{DMA}₃] (3D, MOF 2), where btc = 1,3,5-benzenetricarboxylic acid, DMF = N,N-dimethylformamide, and DMA = dimethylamine, have been crystallized under hydrothermal conditions, from a single reaction. MOF 1 shows an extraordinary OER performance with 175 mV overpotential to attain 10 mA cm^–2 current density with a low Tafel slope value of 80 mV dec^–1, whereas MOF 2 achieves 10 mA cm^–2 current density at 389 mV overpotential. Two different architecture-based MOFs have been synthesized from a single solution for the very first time. Also, the OER activity of MOF 1 overpowers the commercially used RuO₂ and surpasses most of the reported OER electrocatalysts. Post OER characterization of MOF 1 revealed the in situ formation of Co(OH)₂ and CoOOH, acting as active sites for the OER process.