STATIC_URL not working

There is a static context-processor (Version 1.8), which isn't the same as the media one. You need to make sure you have django.core.context_processors.static in your context-processor list, so it can add STATIC_URL to the context.

As commented, for Django 3.0, that is now at django.core.context_processors.static. Django sure has changed a lot since 2011...

From the docs:

If {{ STATIC_URL }} isn't working in your template, you're probably not using RequestContext when rendering the template.

https://docs.djangoproject.com/en/dev/howto/static-files/