Argon ion plasmas are generated by a large dc multicusp plasma chamber, which has a 31.2 cm diameter and 42.5 cm length and is surrounded by 632 ceramic permanent magnet buttons with a maximum magnetic field of about 2.2 kG. A plasma density was measured for four different magnet geometries with a multicusp field configuration using a single cylendrical Langmuir probe. One of four magnet configuration results in the Ar⁺ ion with a maximum plasma density of 2.6x10⁺¹⁰ cm^-3 at the discharge voltage of 50 V and the discharge operating current of 1.0 A with 600 watts of power applied to the tungsten filament and gas pressure inside the chamber of 1.1x10^-3 Torr. With a magnetic field of 7 G at the cusp(s), the plasma can be confined within the chamber to a diameter of 24 cm and uniform along the Z-axis (longitudanal path). Results of the ion density measurement are described.