A fluid cooled electrical ionizer assembly includes a stack of honeycomb sheet-like structures of dielectric material with an electrode between each pair of honeycomb sheet-like structures. Alternate electrodes are electrically coupled together to each other and may be coupled to respective terminals of an electrical circuit. Fluid passages in the honeycomb sheet-like structures provide a place for fluid to affect electrical characteristics of the ionizer assembly and/or to provide for cooling. A method of assembling an ionizer assembly includes placing ionizer subunits including a dielectric honeycomb sheet-like structure and an electrode in parallel planar, overlying relation with the honeycomb. A method of cooling an ionizer assembly of dielectric honeycomb structure and electrodes includes directing a fluid through flow channels in the honeycomb structure.