Southwestern Ontario now has four area codes.
The Canadian Radio-television and Telecommunications Commission (CRTC) introduced the "382" area code on Saturday.
The region, which includes Windsor, London, Woodstock, Sarnia, Chatham-Kent, and Stratford, is now served by the "226," "519," "548," and "382" area codes.
Residents won't notice any difference unless they get a new phone number or call a phone with one, and existing numbers won't change.
The CRTC announced it would add another area code last November.
The Canadian Numbering Administrator said Southwestern Ontario was running out of phone numbers, and the addition will create millions of new ones.
It will only be assigned once numbers associated with the existing area codes run out, sometime this month.
Southwestern Ontario got its first area code, "519," in 1953. The CRTC added "226" in 2006 and "548" in 2016. Demand has increased significantly in recent years as sales of cell phones have jumped.
Three-digit numbers like 211, 311, 411, 611, and 911 will not change.
