Can you still dial 911 in an emergency after you cancel your home telephone service?

It depends on whether the service provider physically disconnected your service or simply turned your service off.

Obviously, if there is no phone line going to your location, you will not be able to make calls, emergency or not. If the service provider just turned your service off in the billing system, you will probably be able to call 911. 9-1-1 can be dialed from any land line that currently has dial tone. If you pick up the handset and there is no dial tone, you will not be able to reach 9-1-1. If there is dial tone, you should be able to reach 9-1-1 even if there is no local or long distance service.