Cobalt-based entropic alloys doped with Ti/Zr/Hf have been investigated in the present work. Thermodynamic calculations have been conducted to predict the phase evolution. The effect of two types of processes (homogenization and cryogenic treatment) on microstructures and properties have been comprehensively analyzed. The compositions and microstructures of the designed alloys in different states have been investigated using multiple techniques. Electrochemical corrosion behaviors at room temperature, high-temperature oxidation behaviors at 600 °C, 800 °C, and 1000 °C, as well as the hardness and compression tests, have been systematically performed. The Ti-doped cobalt-based entropic alloy demonstrated excellent overall properties, including strong electrochemical corrosion resistance, high-temperature oxidation resistance, and a combination of high strength and ductility. The phase map from electron backscatter diffraction (EBSD) indicated that Ti has weaker stability for the formation of the C14-Laves phase compared to the alloying effects of Zr and Hf. The characterization results align with the thermodynamic calculations. This work paves a way for establishing material design strategies to develop advanced alloys with superior performance.