Singapore is about 273 times smaller than South Dakota.

South Dakota is approximately 196,540 sq km, while Singapore is approximately 719 sq km, making Singapore 0.37% the size of South Dakota. Meanwhile, the population of South Dakota is ~814,180 people (5.1 million more people live in Singapore).
Tip: This to-scale comparison of South Dakota vs. Singapore uses the Mercator projection, which distorts the size of regions near the poles.