We evaluated the suitability of Fe40Co30Ni30 as a precursor for Fe-rich FeCoNi-based high-entropy semi-hard magnets. Mechanically alloying the metal powders 40 at.% Fe, 30 at.% Co, and 30 at.% Ni for 12 h effected micron-size Fe40Co30Ni30 powder comprised of nanocrystalline γ phase. Fe40Co30Ni30 evinced semi-hard magnetic properties at room-temperature—saturation magnetization (MS) ~146 Am2/kg and intrinsic coercivity (HCI) ~4.30 kA/m—as well as at below-room-temperatures. The MS at 0 K, μH, and HCI at 0 K were estimated as ~155 Am2/kg, ~1.60 μB, and ~7 kA/m, respectively. Alloy powders after thermal-treatment exhibited tunable semi-hard magnetic behavior at below-room temperatures and room temperature; their magnetic properties were comparable to certain commercial semi-hard magnets. The weighted Euclidean distance-based approach of decision-making proposed the Fe-rich FeCoNi medium-entropy alloy—Fe40Co30Ni30—as a favorable precursor, having an optimal combination of properties, for designing and fabricating novel FeCoNi-based high-entropy semi-hard magnets.