Montgomery County, OH borders Greene near Dayton metropolitan centre giving a 2020 estimated population standing at 535,153 making it the 4th most populous county located in Ohio overall. Its county seat is Dayton with other cities include Kettering & Huber Heights-Dayton itself equates out to Montgomery's largestcity aside from noted country seat. This area had been created from Hamilton and Greene Counties back in 1803 when local citizens petitioned for new administrative boundaries - posthumously named after Revolutionary War General Richard Montgomery command era preceding Thomas Jefferson .