Where is Elizabeth in the end of At World's End? Will gives her his heart to protect and leaves her on some island. Is it Davy Jones' locker?
As per wikia, she is at Port Royal. Check out the epilogue on above link page:
Ten years later, Elizabeth and her son, young Will Turner reside in Port Royal.Young Will sings a pirate song, with Elizabeth following behind. They both stand at the edge of a cliff, looking at the horizon, waiting for the sun to set. Finally, they see a flash of green light as the Flying Dutchman reappears, signifying Will Turner's return from the Land of the Dead.
However, I am not able to understand where it is shown that this place is Port Royal. My understanding for that scene is only that Will is not bounded to ship and uses his one day in ten years to meet Elizabeth who is living somewhere on land with other citizens (not pirates).