This visualization found in Wikimedia.org, shows World War II casualties per country by number and percentage of population, as well as the percentage of military and civilian deaths for the Allied and the Axis Powers.

The countries with the largest number of casualties were the Soviet Union, China, Germany, Poland, and Indonesia. As a percentage of the population, the nations with the  largest number of casualties were Lithuania, Poland, Latvia, Germany, and the Soviet Union.

For the Allied forces, the heaviest casualties were inflicted on the civilian population, whereas the largest number of casualties for the Axis forces were inflicted on the military.