In iron pnictides, high temperature superconductivity emerges after suppressing antiferromagnetism by doping. Here we show that antiferromagnetism in Ca_1-xLa_xFeAs_2 is robust against and even enhanced by doping. Using ^75As-nuclear magnetic resonance and nuclear quadrupole resonance techniques, we find that an antiferromagnetic order occurs below the Néel temperature T_ N = 62 K at a high doping concentration (x = 0.15) where superconductivity sets in at the transition temperature T_ c = 35

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... Unexpectedly, T_ N is enhanced with increasing doping, rising up to T_ N = 70 K at x = 0.24. The obtained phase diagram of this new system enriches the physics of iron-based high-T_ c superconductors.