Missouri is about 756 times bigger than Cook Islands.

Cook Islands is approximately 236 sq km, while Missouri is approximately 178,414 sq km, making Missouri 75,499% larger than Cook Islands. Meanwhile, the population of Cook Islands is ~8,128 people (6.0 million more people live in Missouri).
Tip: This to-scale comparison of Cook Islands vs. Missouri uses the Mercator projection, which distorts the size of regions near the poles.