| Number | Length (km) | Length (mi) | Southern or western terminus | Northern or eastern terminus | Local names | Formed | Removed | Notes |
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 County Road 1 | — | — | St. Clair Parkway inPort Lambton | Highway 40 east of Port Lambton | Lambton Line | — | — | |
 County Road 2 | — | — | St. Clair Parkway inSombra | County Road 79 atCairo | Bentpath Line | — | — | |
 County Road 4 | — | — | St. Clair Parkway inCorunna | County Road 79 north ofAlvinston | Hill Street, Petrolia Line | — | — | Originally called the 10th Line |
 County Road 5 | — | — | Highway 21 nearGrand Bend | County Road 5 (Middlesex County) at theAusable River | Greenway Road | — | — | |
 County Road 6 | — | — | Highway 21 atLambton Shores | County Road 7 (Middlesex County) at theAusable River | Thomson Line | — | — | Easternmost section formerlyHighway 7 |
 County Road 7 | — | — | Michigan Avenue inSarnia | Highway 21 atLambton Shores | Christina Street, Lakeshore Road | — | — | |
 County Road 8 | — | — | County Road 8 (Chatham–Kent) nearFlorence | Highway 402 /Highway 21 nearWarwick | Forest Road, Inwood Road, Shetland Road | — | — | |
 County Road 9 | — | — | County Road 22 /County Road 79 nearWarwick | County Road 79 nearThedford | Northville Road | — | — | |
 County Road 11 | — | — | County Road 7 nearCamlachie | Highway 21 nearForest, Ontario | Aberarder Line | — | — | |
 County Road 12 | — | — | County Road 7 nearForest | County Road 12 (Middlesex County) nearArkona | Townsend Line | — | — | |
 County Road 14 | — | — | County Road 20 /County Road 31 atSarnia | County Road 22 nearWyoming | Churchill Line | — | — | |
 County Road 15 | — | — | County Road 12 (Middlesex County) nearRutherford | County Road 21 in Rutherford | Dawn Mills Road | — | — | |
 County Road 16 | — | — | Vidal Street (southbound) / Brock Street (northbound) inSarnia | Highway 40 /County Road 22 in Sarnia | London Road | — | — | Easternmost section formerlyHighway 402 |
 County Road 17 | — | — | Vidal Street North (southbound) / Brock Street (northbound) inSarnia | Highway 40 in Sarnia | Wellington Street | — | — | |
 County Road 18 | — | — | County Road 79 nearPort Franks | County Road 18 (Middlesex County) at theAusable River | Bog Line | — | — | |
 County Road 19 | — | — | County Road 29 inSarnia | County Road 27 at Sarnia | Michigan Avenue, Michigan Line | — | — | |
 County Road 20 | — | — | Highway 40 atSarnia | County Road 4 near Sarnia | Plank Road | — | — | |
 County Road 21 | — | — | County Road 21 (Chatham–Kent) nearDresden | Highway 402 /County Road 30 atReece's Corners | Oil Heritage Road, Broadway Street | — | — | Formerly southern part ofHighway 21 |
 County Road 22 | — | — | Highway 40 /County Road 16 inSarnia | County Road 22 (Middlesex County) nearWarwick | London Line | — | — | FormerlyHighway 22 and westernmost section ofHighway 7 |
 County Road 23 | — | — | County Road 79 inAlvinston | County Road 80 near Alvinston | Railroad Street, River Street | — | — | |
 County Road 25 | — | — | Vidal Street (southbound) / Brock Street (northbound) inSarnia | County Road 39 /County Road 79 inWatford | Confederation Line | — | — | |
 County Road 26 | — | — | County Road 44 (Chatham–Kent) nearTupperville | County Road 7 atBrights Grove | Mandaumin Road | — | — | |
 County Road 27 | — | — | Highway 402 /Highway 40 atSarnia | County Road 7 at Sarnia | Modeland Road | — | — | |
 County Road 28 | — | — | St. Clair Parkway nearSombra | Highway 40 near Sombra | Holt Line | — | — | |
 County Road 29 | — | — | Highway 40 atSarnia | County Road 7 at Sarnia | Indian Road | — | — | |
 County Road 30 | — | — | Highway 402 /County Road 21 atReece's Corners | County Road 7 nearCamlachie | Oil Heritage Road | — | — | |
 County Road 31 | — | — | County Road 31 (Chatham–Kent) nearWallaceburg | County Road 14 /County Road 20 atSarnia | Kimball Road | — | — | |
 County Road 33 | — | — | County Road 33 (Chatham–Kent) nearWallaceburg | Vidal Street andCounty Road 34 atSarnia | St. Clair Parkway | 01977-01-011977 | 01984-01-011984 | FormerlyHighway 40; turned back in stages |
 County Road 34 | — | — | St. Clair Parkway atSarnia | Highway 40 at Sarnia | Churchill Line | 01993-01-011993 | current | Formerly Highway 40 andHighway 40B |
 County Road 35 | — | — | St. Clair Parkway nearCorunna | Highway 40 near Corunna | La Salle Line | — | — | |
 County Road 36 | — | — | St. Clair Parkway nearCourtright | Highway 40 near Courtright | Bickford Line | — | — | |
 County Road 39 | — | — | County Road 79 inWatford | County Road 39 (Middlesex County) nearKerwood | Confederation Line | — | — | |
 County Road 79 | — | — | County Road 16 (Chatham–Kent) nearBothwell | Highway 21 nearPort Franks | Northville Road, Arkona Road, Egremont Road, Nauvoo Road, Cairo Road | 01998-01-011998 | current | FormerlyHighway 79 andHighway 7 |
 County Road 80 | — | — | St. Clair Parkway inCourtright | County Road 80 (Middlesex County) nearAlvinston | Courtright Line | — | — | FormerlyHighway 80 |
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