Guinea-Bissau is about 4 times smaller than Illinois.

Illinois is approximately 143,961 sq km, while Guinea-Bissau is approximately 36,125 sq km, making Guinea-Bissau 25.09% the size of Illinois. Meanwhile, the population of Illinois is ~12.8 million people (10.8 million fewer people live in Guinea-Bissau).
Tip: This to-scale comparison of Illinois vs. Guinea-Bissau uses the Mercator projection, which distorts the size of regions near the poles.