Radnor is an unincorporated community and census-designated place in central Radnor Township, Delaware County, Ohio, United States. As …Radnor is an unincorporated community and census-designated place in central Radnor Township, Delaware County, Ohio, United States. As of the 2010 census it had a population of 201. Radnor has a post office with the ZIP code of 43066. It lies along State Route 203 at its intersection with Radnor Road.