The effect of nitrogen on the microstructure and mechanical behavior of several Co-free high entropy alloys (HEAs) from the CrFeMnNi family was studied. Alloy design approach, based on thermodynamic computations, was implemented to obtain alloys with a high chromium content, a high nitrogen solubility as well as good austenite stability. An optimisation was made to meet selected criteria which led to three compositions with different nickel contents (Cr₂₀Fe₄₀Mn₁₅Ni₂₅, Cr₂₀Fe₄₄Mn₁₅Ni₂₁, and Cr₂₀Fe₄₇Mn₁₅Ni₁₈) optimised for, respectively, 0.4, 0.5 and 0.6 wt% N. Such optimised alloys were elaborated and compared with another Co-free HEA (Cr1₄Fe₄₆Mn₁₇Ni₂₃) doped with 0.11–0.29 wt% N. It was shown that up to 0.56 wt% N could be dissolved in the matrixes in agreement with their computed high nitrogen solubility. The differences in chemical composition between the four studied matrixes did not lead to any change in behavior in presence of nitrogen: the lattice parameter expansion and mechanical resistances (yield strength and tensile strength) evolve linearly with nitrogen addition, up to at least 0.56 wt%. Especially, a significant effect of nitrogen content on strain-hardening was observed and was attributed to the formation of nanotwins in nitrogen-rich alloys.