The plasma parameters in the 2.45 GHz electron cyclotron resonance (ECR) proton ion source have been measured and optimized at low pressures. These parameters are important as they are related to the beam parameters of the ion source. A detailed plasma characterization study has been conducted using hydrogen as a working gas in the operating pressure and power range 10⁻⁴–10⁻³ mbar, 400–1000 W of the ion source, respectively. The plasma parameters have been measured in the ECR zone of the plasma chamber. An automatic Langmuir probe and data acquisition system has been used to measure these parameters. In the above-mentioned power and pressure range, the plasma density, plasma electron temperature, and plasma potential measured are in the range 4×10¹¹ – 6.5×10¹¹ cm⁻³, 4–11 eV, and 30–40 V, respectively. The variation of plasma parameters with neutral gas pressure is studied for different microwave powers. A 0-D (global) model has been developed to compare the measured plasma parameter data with the calculated ones. The ion species content in the plasma was measured after extraction using a magnetic mass analyzer and a Faraday cup. A plasma-based model has been developed to compare the measured ion species fraction data with the calculated ones by taking the measured ECR plasma parameters as input.