This is a list of numbered roads in Northumberland County, Ontario.
| County Road # | Local Name(s) | Southern/Western Terminus | Northern/Eastern Terminus | Settlements served | Additional Notes |
|---|---|---|---|---|---|
| 2 | County Road 2, various town streets (see notes) | East Townline Road | Walt Street | Welcome, Port Hope, Cobourg, Grafton, Colborne, Brighton, Smithfield | Part of old King's Highway 2. Also known as Toronto Road, Ridout Street, Walton Street, Mill Street and Peter Street, Port Hope; William Street and King Street, Cobourg; Toronto Street and King Street, Colborne; and Main Street and Elizabeth Street, Brighton. |
| 8 | County Road 8 | County Road 30 | Wingfield Road | Campbellford, English Line, Hoards | |
| 9 | Ganaraska Road | Cold Springs Camp Road | County Road 45 | Elizabethville, Garden Hill, Bewdley | continues as Durham Road 9 to Kirby |
| 10 | County Road 10 | County Road 2 | Challice 1st Line | Welcome, Perrytown, Thomstown | continues as Peterborough County/Kawartha Lakes Road 10 to Pigeon Lake Road |
| 15 | Harwood Road | County Road 45 | County Road 18 | Harwood | |
| 18 | County Road 18 Burnham Street |
County Road 2 | County Road 45 | Cobourg, Cold Springs, Gores Landing, Harwood, Alderville | |
| 20 | Elgin Street Brook Road |
County Road 18 | County Road 2 | Cobourg | |
| 21 | County Road 21 | County Road 25 | County Road 30 | Tubbs Corners, Dundonald, Hilton | |
| 22 | County Road 22 | County Road 45 | County Road 25 | Centreton, Castleton | |
| 23 | County Road 23 Lyle Street |
County Road 2 | County Road 22 | Centreton, Grafton | |
| 24 | County Road 24 | County Road 45 | County Road 25 | Roseneath, Dartford | |
| 25 | County Road 25 | County Road 2 | the Trent River | Colborne, Purdy Corners, Tubbs Corners, Castleton, Morganston, Warkworth, Hastings | |
| 26 | County Road 26 | County Road 30 | County Road 41 | Spring Valley | |
| 27 | County Road 27 | County Road 25 | County Road 30 | Morganston, Codrington | |
| 28 | County Road 28 Ontario Street |
County Road 2 | Hannah Road | Port Hope, Dale, Rosemount, Bewdley | continues as Peterborough County Road 28 to King's Highway 115 |
| 29 | County Road 29 | Regional Road 45 | Percy Boom Road | Burnley, Warkworth | |
| 30 | County Road 30 | County Road 2 | Browns Line Road | Brighton, Spring Valley, Hilton, Orland, Codrington, Meyersburg, Campbellford, West Corners, Trent River | |
| 31 | Lakeport Road | Town Line Road | County Road 2 | Colborne, Lakeport | |
| 33 | Merrill Road | County Road 45 | 7th Line | McCracken Landing | |
| 35 | County Road 35 | County Road 25 | County Road 30 | Godolphin, West Corners | |
| 38 | County Road 38 | County Road 8 | Rylstone Road | Campbellford, Pethericks Corners | |
| 41 | New Wooler Road | County Road 30 | Dalmas Road | Orland | |
| 45 | County Road 45 Division Street |
County Road 2 | County Road 25 | Cobourg, Creighton Heights, Baltimore, Fenella, Alderville, Roseneath, Hastings | |
| 50 | County Road 50 | County Road 30 | Trent River Road | Campbellford, Healey Falls | |
| 64 | County Road 64 Prince Edward Street |
County Road 2 | Stoney Point Road | Brighton, Gosport | continues as Hastings County Road 64 to Loyalist Parkway |
| 65 | County Road 65 | County Road 2 | County Road 9 | Osaca, Elizabethville | |
| 66 | Ontario Street | Presqu'ile Parkway | County Road 2 | Brighton, Presqu'ile Provincial Park | |
| 70 | Jocelyn Street | County Road 2 | County Road 28 | Port Hope | |
| 74 | Dale Road | County Road 10 | County Road 45 | Welcome, Dale, Precious Corners, Baltimore |
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