Missouri is about 290 times bigger than Saint Lucia.

Saint Lucia is approximately 616 sq km, while Missouri is approximately 178,414 sq km, making Missouri 28,863% larger than Saint Lucia. Meanwhile, the population of Saint Lucia is ~167,122 people (5.8 million more people live in Missouri).
Tip: This to-scale comparison of Saint Lucia vs. Missouri uses the Mercator projection, which distorts the size of regions near the poles.