July 9 (UPI) -- Texas Gov. Greg Abbott on Wednesday ordered state legislators to convene a special session on Monday as the death toll rose to at least 120 people and 172 reported missing in Fourth of July flooding in theHill Country.

It's the deadliest flash flood in the United States since 1976 in Thompson Canyon, Colo., when 144 people were killed, according to the Weather Channel. In 1972, 238 died in flooding in Black Hills, S.D.

Kerr County has the most fatalities with 96, including 36 children, and 161 missing, CNN reported. One of the dead was a 20-month-old Austin boy who died after his family's home was inundated by water from the Guadalupe River, which runs 230 miles between Austin and San Antonio.

At least 27 of those fatalities were children and counselors at Camp Mystic, a girls Christian camp along the Guadalupe River, which swelled to 20 feet.

Among the missing are five campers and one counselor from Camp Mystic, officials said.