Mississippi is about 686 times bigger than District of Columbia.

District of Columbia is approximately 177 sq km, while Mississippi is approximately 121,489 sq km, making Mississippi 68,538% larger than District of Columbia. Meanwhile, the population of District of Columbia is ~601,723 people (2.4 million more people live in Mississippi).
Tip: This to-scale comparison of District of Columbia vs. Mississippi uses the Mercator projection, which distorts the size of regions near the poles.