South Dakota is about 4 times smaller than Turkey.

Turkey is approximately 783,562 sq km, while South Dakota is approximately 196,540 sq km, making South Dakota 25.08% the size of Turkey. Meanwhile, the population of Turkey is ~83.0 million people (82.2 million fewer people live in South Dakota).
Tip: This to-scale comparison of Turkey vs. South Dakota uses the Mercator projection, which distorts the size of regions near the poles.