The province of Ontario, Canada is currently served by a total of 17 area codes:
These Ontario area codes overlay (cover the same geographic area). The first code listed is the parent code. Overlay area codes are added when no more phone numbers are available in an existing Numbering Plan Area.
| City | Area code(s) |
|---|---|
| Ajax | 905/289/365/742 |
| Aurora | 905/289/365/742 |
| Barrie | 705/249/683 |
| Belleville | 613/343/753 |
| Brampton | 905/289/365/742 |
| Brantford | 519/226/548 |
| Burlington | 905/289/365/742 |
| Caledon | 905/289/365/742 |
| Cambridge | 519/226/548 |
| Cornwall | 613/343/753 |
| Guelph | 519/226/548 |
| Haldimand County | 905/289/365/742 |
| Hamilton | 905/289/365/742 |
| Innisfil | 905/289/365/742 |
| Kingston | 613/343/753 |
| Kitchener | 519/226/548 |
| Leamington | 519/226/548 |
| London | 519/226/548 |
| Milton | 905/289/365/742 |
| Mississauga | 905/289/365/742 |
| Newmarket | 905/289/365/742 |
| Niagara Falls | 905/289/365/742 |
| Norfolk County | 519/226/548 |
| North Bay | 705/249/683 |
| Oakville | 905/289/365/742 |
| Orillia | 705/249/683 |
| Oshawa | 905/289/365/742 |
| Ottawa | 613/343/753 |
| Peterborough | 705/249/683 |
| Pickering | 905/289/365/742 |
| Quinte West | 613/343/753 |
| Richmond Hill | 905/289/365/742 |
| Sarnia | 519/226/548 |
| Sault Ste Marie | 705/249/683 |
| St Catharines | 905/289/365/742 |
| St Thomas | 519/226/548 |
| Stratford | 519/226/548 |
| Sudbury | 705/249/683 |
| Thunder Bay | 807 |
| Timmins | 705/249/683 |
| Toronto | 416/647/437 |
| Vaughan | 905/289/365/742 |
| Waterloo | 519/226/548 |
| Windsor | 519/226/548 |
| Woodstock | 519/226/548 |