We present muon-spin-rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic (AF) zigzag chain compounds, Na_xCa_1-xV₂O₄. In this family, we explore the magnetic properties from the metallic NaV₂O₄ to the insulating CaV₂O₄. We find a critical x_c (∼0.833) which separates the low and high Na-concentration-dependent transition temperature and its magnetic ground state. In the x < x_ccompounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the x > x_c compounds, multiple subphases appear with temperature and x. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.