In this paper, an elephant herding optimization (EHO) based optimal proportional-integral-derivative (PID) controller is proposed for level control of three tank system. The integral-square-error (ISE) of unit step response is minimized for obtaining optimal controller parameters. The ISE is obtained with the help of alpha and beta tables. The EHO algorithm is utilized for minimizing the ISE. The results obtained using proposed methods are compared with other techniques. It is found that the proposed technique performs better in comparison to others.