This paper presents a distributed open-loop optogenetic control for suppression of epileptiform activity in a neural population model of cortex. In epilepsy, cortical seizures or epileptiform activities occur when pyramidal cells become hyper-excitable due to the loss of inhibitory interneurons. A straightforward way to suppress these epileptiform activities is to inhibit pyramidal cells by exciting interneurons. Thus, in this paper, the inhibitory neural population is targeted for the application of open-loop optogenetic control. By introducing computational model of the light-gated Channelrhodopsin-2 (ChR2) ion channels into the well-known Wilson-Cowan model, we first establish a neural population model for optogenetic control of cortical dynamics. Then, we investigate the effects of open-loop optogenetic control parameters (irradiance intensity and pulse duration) on the control performance. Finally, we use a spatially distributed control strategy to normalize cortical dynamics with minimum optical stimulations. The simulation results demonstrate the effectiveness of our propose control method for suppression of epileptiform activities.