Belarus is about 1.4 times bigger than Illinois.

Illinois is approximately 143,961 sq km, while Belarus is approximately 207,600 sq km, making Belarus 44% larger than Illinois. Meanwhile, the population of Illinois is ~12.8 million people (3.4 million fewer people live in Belarus).
Tip: This to-scale comparison of Illinois vs. Belarus uses the Mercator projection, which distorts the size of regions near the poles.