South Dakota is around the same size as Belarus.

Belarus is approximately 207,600 sq km, while South Dakota is approximately 196,540 sq km, making South Dakota 94.67% the size of Belarus. Meanwhile, the population of Belarus is ~9.4 million people (8.6 million fewer people live in South Dakota).
Tip: This to-scale comparison of Belarus vs. South Dakota uses the Mercator projection, which distorts the size of regions near the poles.