South Dakota is about 273 times bigger than Singapore.

Singapore is approximately 719 sq km, while South Dakota is approximately 196,540 sq km, making South Dakota 27,228% larger than Singapore. Meanwhile, the population of Singapore is ~5.9 million people (5.1 million fewer people live in South Dakota).
Tip: This to-scale comparison of Singapore vs. South Dakota uses the Mercator projection, which distorts the size of regions near the poles.