Missouri, Illinois, and Kansas were among the states hit.
"These 29 reported tornadoes occurred late Monday afternoon into Monday night," ABC News meteorologist Daniel Manzo said. "This made a for a very perilous situation for millions of Americans ... in addition to the tornadoes, giant tennis ball sized hail was reported across eastern Kansas and Missouri."
Chief Carl Scarborough of the Sni Valley Fire Protection District in Oak Grove, Missouri, told ABC News Monday night that between 100 and 200 people have been displaced from their homes, but that figure may increase. He added that "dozens and dozens" of homes have sustained moderate to severe damage in Oak Grove, with a significant number of additional sustaining light to minimal damage.
Scarborough said he is aware of 12 people who were treated for injuries, three of whom were transported to the hospital. None of the injuries were life-threatening.
Most of Oak Grove -- located about 30 miles east of Kansas City -- was without power, as of Monday night, as power lines were down as a result of falling trees and airborne debris.
In Smithville, Missouri, located about 22 miles north of Kansas City, police Chief Jason Lockridge told The Associated Press that 20 to 25 homes were damaged. Planes and hangars at the Johnson County Executive Airport in Olathe, Kansas, were also damaged.
The city of Smithville posted on it Facebook page that "one person was injured but was not transported to the hospital."
Kansas City Power & Light reported on its website early Tuesday morning that about 40,000 customers were without power. That's down from more than 100,000 late Monday night.
ABC News' Rachel Katz contributed to this report.