We present thermal models of the 24 Ma Cocos plate subducting under the Caribbean plate at the Nicoya Peninsula, Costa Rica. Our modeling incorporates the effect of hydrothermal cooling of the seafloor and the absence of an accretionary prism. Initial geotherms of the incoming plate, representing different effective cooling depths of hydrothermal circulation, affect the thermal structure and temperatures along the main subduction thrust. Excluding the deforming prism results in a higher heat flow immediately landward of the trench than previous models and therefore significant frictional heating is not required. Conductive plate cooling over-predicts heat flow across the frontal forearc. With no or very low frictional heating, models with hydrothermal cooling to depths of 2 km under-predicts the heat flow. Comparisons with recently determined hypocenter locations indicate that the updip limit of seismicity is consistent with temperatures between 100¿--150¿C, but there are large along-strike variations in both the seismicity and thermal regime.