Storing Checkbox Cookie?

I know how to create cookies etc.. I've got to the point where the checkbox is stored in a cookie. But how can i make it so that when the checkbox is checked and the person leaves the page, when they come back i need the checkbox to still be checked(ticked) instead of blank (the checkbox being ticked will run a function to do something else..).

do i need an if statement? how would i do this? is this right?

if(cookie is set){
make the checkbox checked
}