Of all the places mentioned in Mark 7:31 (Tyre, Sidon, Sea of Galilee, and Decapolis) it is unclear exactly where this miracle took place.
Here are some of the suggestions:
The Decapolis is mentioned last in the list of places. This could mean that Mark wanted his readers to understand that the miracle happened here.
Jesus left Tyre, passed through Sidon and the Decapolis and reached his destination—the Sea of Galilee where the miracle took place.1
When looking at the Greek text (the verb, the preposition, and the order of the words) and comparing it to the rest of Mark, it looks like the miracle took place at the Sea of Galilee. A literal translation of Mark 7:31 would look like this:
And having departed from the regions of Tyre, he again came to the Sea of Galilee by way of Sidon through the middle of the Decapolis.
In every other instance in Mark where we find he/they came/come to, the following incident/event takes place in the location described by the to
.2
31 Then he returned from the region of Tyre and went through Sidon to the Sea of Galilee, in the region of the Decapolis.