The most populated counties in Ohio are Cuyahoga, Franklin and Hamilton, and the license plate codes are 18 for Cuyahoga, 25 for Franklin and 31 for Hamilton. Summit County uses county code 77 and Montgomery County uses 57.
Ohio uses numerical county-coding on its license plates to designate the vehicle's county of registration. Drivers can find their county code on a sticker placed in the lower left corner of both the front and rear license plates. The sticker displays the county's full name below the number. The state assigned numbers to each county alphabetically. Adams County is the first alphabetically and has number 01, while Wyandot County is last alphabetically and has number 88. The least populated counties in Ohio are Vinton, Noble and Monroe. Vinton has county code 82, Noble has 61 and Monroe has 56.
Ohio issued its first license plates in 1908. The first plates were dark blue with white lettering and displayed a stylized state abbreviation rather than the entire state name. New plates issued in 1910 had a wood grain background with white lettering. Ohio's current license plate features a word cloud background with 46 different slogans and a red triangle to symbolize an airplane wing. The state began using this plate on April 15, 2013. Ohio requires that drivers convicted of Driving Under the Influence with limited driving privileges display a yellow and red license plate on their vehicle.