In the late 1990s, when the provincial government downloaded many portions of Ontario highways to the municipalities, Wellington County became responsible for portions of former highways 9, 23, 24 and 25.
Road numbers in Wellington County mainly follow a system in which the numbers correspond to the township in which the road has its county terminus.
Roads 1-6 are in Minto; 7-12 in Mapleton; 14-16 in Wellington North; 17-21 in Centre Wellington; 22-26 in Erin; 27-29 in former Eramosa Township (now a part of Guelph-Eramosa); and 30-41 in former Guelph Township (also now a part of Guelph-Eramosa) and Puslinch, many of which are roads that originate in the City of Guelph.
Highways 86 and 87 are named for the county road of the same name that continue past the boundaries of Waterloo Region and Huron County respectively.
All other roads were numbered after this system was put into place, and are mostly very short routes connecting villages or other points of interest to the main county road system.