Russia is not Europe, It is niether Europe nor Asia. Poland is in Eastern Europe
Russia is in Europe. Its called a transcontinental state.
Eastern Europe is all the former states in Europe from USSR.
Poland is center of the main land (geograhpically) and is an Eastern European country.
Although Poland is more 'westernized' than other EE.
Poland is Eastern European country seems fine
Poles might get upset when its phrased differently:
Poland is an Eastern European country which is backwards (from communism).
The last is a bit more 'in your face'