24 Countries with Biggest Population Decline (2000–2025). 1. #Ukraine: -33% 2. Marshall Islands: -29% 3. #Bulgaria: -23% 4. #Latvia: -22% 5. #Moldova: -19% 6. #Lithuania: -18% 7. Puerto Rico: -17% 8. #Romania: -16% 9. #Serbia: -13% 10. Albania: -13% 11. Croatia: -12% 12. Micronesia: -11% 13. #Georgia: -10% 14. North Macedonia: -10% 15. #Belarus: -9% 16. Bosnia & Herzegovina: -8% 17. #Hungary: -7% 18. Palau: -5% 19. #Poland: -5% 20. #Greece: -4% 21. Armenia: -3% 22.