Who typically lived in Decapolis?

Assuming you mean the Decapolis of the Biblical New Testament, the following might help.

Decapolis was the name given to 10 cities in a region in Jordan and Palestine that were founded mainly between 323BC and the Roman arrival in about 60BC. Note, there is likely to have been more than 10 cities.

The cities were generally founded by Hellenists (Greeks) and other peoples of the Greek culture. They were made up of Greeks and local people, usually Jewish and the two groups lived together fairly well, and their culture and religions began to blend with time.

The same mix of peoples occupied the cities when the Romans arrived. The cities became powerful "City-States" and began to take on the Roman culture and way of life.