We have developed multiple inductively coupled plasma (ICP) sources for large-area processes. These multiple ICP sources are composed of 16 -small ICP sources in parallel. Simulations were performed to design multiple ICP sources that could generate uniform plasma by adjusting the lengths of the coaxial transmission line and the ground-return paths. Plasma distribution was measured with an array of ion saturation probes. We demonstrated that it is possible to generate uniform plasma when equal power is supplied to each source by equalizing the lengths of the coaxial transmission line as well as maintaining the same length for all the ground-return paths. To distribute equal power to each source, the impedance of the ground path is crucial because the total impedance of a small ICP source is strongly dependent on the distance between the power supply and the source. We confirmed that this approach enables multiple ICP sources to generate uniform plasma without the need for additional control equipment.