Russia

From CaseyPedia

A large and imposing country found between China and Poland. Casey Serin is often inaccurately assumed to be Russian, though as a native of Uzbekistan he would have been born in the Soviet Union, a collection of states dominated by Russia. His native language is also Russian.

Another former Soviet state is Ukraine, and people often confuse the two when describing Casey's origins, but they are entirely separate countries situated many thousands of miles apart.