There is a WebElement property called is_selected(), and for a check box this indicates whether or not it is checked. Therefore you can verify if it is checked/unchecked by doing something like this:
driver.find_element_by_name('<check_box_name>').is_selected()
or
driver.find_element_by_id('<check_box_id>').is_selected()
I remember having the same issue not being able to find documentation. It’s easier to find once you know the name (here are some docs, is_selected is towards the bottom), but the way I have gone about trying to find different options/properties for Selenium objects is to just drop dir(some_object) in the code and see what options come up (this is how is_selected appeared).