[sheepdog 44]

I really hate hills sometimes! I probably climb over 3,000 feet a day in elevation gain and loss. Hypermiling tip: consider moving to the gulf, Illinois, or Delaware. Kansas?

What is the US state that is the most flat?

"Flattest Roads: Louisiana is the flattest state, though Florida and Illinois follow close behind. Louisiana is interesting because you can drive for 100 miles straight north and gain less than 100 feet in elevation. There's standing water on the sides of the road (and armadillo roadkill) just about everywhere in Louisiana. And speaking of flat, the Florida Everglades is probably the flattest region in the U.S. Illinois is also pancake-flat but, unlike Florida and Louisiana, it's not interesting at all."
The Best and Worst of the 50 States

But,
"If you measure flatness by the difference between the highest and lowest elevations, Kansas is 22nd, with Florida leading the way. If you measure it using elevation changes in 1-kilometer sections, it is 32nd, with Delaware the flattest."
Holy hotcakes! Study finds Kansas flatter than pancake / LJWorld.com

I grew up in Florida and can't imagine a flatter state. It does have rolling hills in the center. Since the experts can't agree on how to measure, so we probably won't get a definitive answer.

Much of the state south of Orlando is low-lying and fairly level; however, some places, such as Clearwater, feature vistas that rise 50 to 100 feet (15 – 30 m) above the water. Much of Central and North Florida, typically 25 miles (40 km) or more away from the coastline, features rolling hills with elevations ranging from 100 to 250 feet (30 – 76 m). The highest point in peninsular Florida, Sugarloaf Mountain, is a 312-foot (95 m) peak in Lake County. . . . The total area of Florida is 65,795 sq mi
(170,304 km²).

Florida - Wikipedia, the free encyclopedia

Florida's highest point is Britton Hill in Walton County - 345 feet (105 m) above sea level - and the lowest highpoint of any U.S. state. Florida has no mountains nor high hills. Therefore, when you consider elevation per area, my vote goes to Florida.