Phone prefixes in Thornhill, ON

In numbers

In-service prefixes

71

Telephone numbers covered

710,000

Carriers

18

Area codes

4

Provinces and territories

1

First assignment

January 7, 2000

Most recent assignment

May 27, 2025

Thornhill’s share of its area codes

Within area code 905, Thornhill accounts for only 28 of 773 prefixes (3.6%): the code is dominated by Hamilton and spread over 94 rate centres. Within area code 365, Thornhill accounts for only 24 of 706 prefixes (3.4%): the code is dominated by Markham and spread over 88 rate centres. Within area code 289, Thornhill accounts for only 16 of 772 prefixes (2.1%): the code is dominated by Hamilton and spread over 87 rate centres. Within area code 742, Thornhill accounts for only 3 of 148 prefixes (2.0%): the code is dominated by Brampton and spread over 68 rate centres.

Who holds these numbers

Bell Canada holds the largest share at 20 prefixes, 28.2% of the total, ahead of 17 other carriers. Code by code: in 905, Bell Canada leads with 19 of 28 prefixes ahead of 4 others; in 365, Iristel Inc. leads with 17 of 24 prefixes ahead of 7 others; in 289, Fibernetics Corporation leads with 3 of 16 prefixes ahead of 9 others; in 742, Fibernetics Corporation leads with 1 of 3 prefixes ahead of 2 others. No carrier holds prefixes in every one of Thornhill’s 4 area codes, while 11 appear in just one.

Wireless and wireline

1 of Thornhill’s 71 prefixes (1.4%) are held by carriers whose registered name marks a wireless business: Fido Solutions Inc. Wireline prefixes still outnumber them, carried by Bell Canada, Iristel Inc, Rogers Communications Canada Inc. (Cable) and Fibernetics Corporation. This is a sort by name, not a licence lookup, and a mobile prefix may have been ported to another network since.

How the allocation was built up

Thornhill’s dated assignments run from 2000 to 2025. The busiest period was 2020–2024, when 17 prefixes went to 5 carriers. 20 prefixes (28%) carry no date in the register: these are the historic pre-1999 assignments, the wireline bedrock of the rate centre. Since 2020 another 18 prefixes have been added, so the rate centre is still growing.

Thornhill’s oldest prefixes, the ones the register leaves undated, belong to Bell Canada and Rogers Communications Canada Inc. (Cable): these carriers made up the landscape before competition arrived. The first dated assignment went to Zayo Canada Inc. in 2000. The most recent arrivals are Cogeco Connexion Inc. (2025), FGLTEL Inc. (2022) and Beanfield Technologies Inc. (2021), a sign that new carriers are still asking for numbers in Thornhill.

Thornhill’s 71 prefixes provide 710,000 numbers, which corresponds to a mid-sized city or a well-established suburb that every major carrier wants a slice of.

No single carrier dominates Thornhill: the leader, Bell Canada, holds only 28.2% of the prefixes against 17 competitors, a sign of a highly fragmented market where cable companies, mobility brands and VoIP providers weigh as much as the incumbent.

Demand remains steady: 35.3% of the dated prefixes go back to the last ten years, the most active period being 2020–2024. The rate centre is growing at a regular rather than explosive pace.

20 undated in the register.

Dialling a Thornhill number

Thornhill is served by 4 overlaid area codes (905, 365, 289 and 742). A 742 number is no more “out of town” than a 905 one; from abroad, dial +1 and the full ten digits.

The numbering neighbourhood

Thornhill shares area codes 905, 365, 289 and 742 with at least 20 other rate centres, including Hamilton, Brampton, Oshawa, St. Catharines-Thorold, Oakville, Markham, Ajax-Pickering and Cooksville. The largest of them, Hamilton, holds 222 prefixes in 289, 365, 742 and 905; the smallest on the list, Maple, has just 28.

What a Thornhill number tells you

A number attached to Thornhill tells you that its prefix was issued to a carrier for this rate centre in Ontario, most often Bell Canada. It does not tell you where the handset is today: a subscriber may have ported the number to any of the 18 carriers present here or to a VoIP service usable anywhere. Nor does it tell you who is calling: caller ID can be spoofed, and an Ontario area code is easy to borrow to look local.

Reading a register entry for Thornhill: code 905-532 is recorded for Bell Canada, so every 905-532-XXXX number (10,000 possible) descends from that assignment. “Thornhill, Ontario” there names a rate centre, not a municipality, and several area codes overlay it.

Every Thornhill prefix

Each row is an in-service central-office code recorded for Thornhill, with its original holder and year of assignment.

Had a call from a Thornhill number?

No clear pattern in reports on these numbers yet. If a call worried you:

1. Call back on a number you trust

   If a caller says they are your bank, the Canada Revenue Agency, a courier or your phone company, hang up and call the organization on the number from its website or your statement, never the number that called you. Caller ID can be faked.

2. Report the fraud

   Report the call or text to the Canadian Anti-Fraud Centre online or at 1-888-495-8501. If you lost money or gave out personal details, tell your bank first, then your local police.

   Report to the Canadian Anti-Fraud Centre ↗

3. Register on the National Do Not Call List

   Registering a landline or mobile on the National DNCL is free. Registered charities, political parties, newspapers and companies you already do business with may still call.

   National Do Not Call List ↗Who can still call you ↗

4. Forward suspicious texts to 7726

   Forward a scam or spam text to 7726 (SPAM on the keypad). It's free, and your carrier uses it to block the sender. Don't tap links or reply.

   Get Cyber Safe: forwarding to 7726 ↗

Allocated prefixes

All 71 in-service prefixes, grouped by rate centre.

Elsewhere in Ontario