Northern Mariana Islands is about 310 times smaller than Illinois.

Illinois is approximately 143,961 sq km, while Northern Mariana Islands is approximately 464 sq km, making Northern Mariana Islands 0.32% the size of Illinois. Meanwhile, the population of Illinois is ~12.8 million people (12.8 million fewer people live in Northern Mariana Islands).
Tip: This to-scale comparison of Illinois vs. Northern Mariana Islands uses the Mercator projection, which distorts the size of regions near the poles.