District of Columbia is about 813 times smaller than Illinois.

Illinois is approximately 143,961 sq km, while District of Columbia is approximately 177 sq km, making District of Columbia 0.12% the size of Illinois. Meanwhile, the population of Illinois is ~12.8 million people (12.2 million fewer people live in District of Columbia).
Tip: This to-scale comparison of Illinois vs. District of Columbia uses the Mercator projection, which distorts the size of regions near the poles.