Heeey. Remember how Grandma's farm was discussed earlier in this thread? And the relation between it and Duckburg? Well, I just read Hobblin' Goblins (W DD 26-03) by Barks, in which HDL say that it's 5 miles (~8 km) from Donald's house to Grandma's farm. The story doesn't give any information about whether the farm is a part of Duckburg or not... but still.
Given the history land ownership in the area, you could say that Duckburg is a part of Grandma's farm.