Saint Lucia is about 290 times smaller than Missouri.

Missouri is approximately 178,414 sq km, while Saint Lucia is approximately 616 sq km, making Saint Lucia 0.35% the size of Missouri. Meanwhile, the population of Missouri is ~6.0 million people (5.8 million fewer people live in Saint Lucia).
Tip: This to-scale comparison of Missouri vs. Saint Lucia uses the Mercator projection, which distorts the size of regions near the poles.