At least six people have died in flooding from torrential rain across large areas of Texas, and emergency workers were searching for an 11-year-old boy who was swept away in a storm-swollen creek in Kansas, the authorities said on Monday.

Record-breaking rain since the middle of last week has swallowed cars, damaged houses and led to the evacuation of 2,600 inmates. Thunderstorms brought more troubles to areas already saturated by other recent storms.

In an area including San Antonio and Austin, Tex., the heavy rain could not soak into the limestone and sandstone that characterize the Hill Country region, leading narrow creeks to brim with fast-running waters.

Since Wednesday, the thunderstorms have dropped pockets of intensely heavy rain, or “rain bombs,” as meteorologists call them.

These have circulated through East Texas, Dallas and Corpus Christi, along with Austin and San Antonio, hitting some parts harder than others, said Kurt Van Speybroeck, a National Weather Service meteorologist.

As a result, rainfall has ranged from four inches in parts of the Dallas-Fort Worth area to 30 inches in Washington County, the authorities said.

“Everybody has seen some impact,” Mr. Van Speybroeck said. “It has been moving all around, but several locations around the state have been taking it on the chin.”

In coastal Brazoria County, where the Brazos River empties into the Gulf of Mexico, 2,600 inmates from two prisons in Rosharon were evacuated on Sunday to facilities in three nearby counties because the river was expected to reach historic flood levels, said Jason Clark, a spokesman for the Texas Department of Criminal Justice.

Texas’ terrain and location make parts of the state prone to unruly weather. Its proximity to a flow of moist air from the Gulf of Mexico sets the stage for heavy rain, and the high potential for rapid runoff in the Hill Country makes it vulnerable to flash floods, said Lamont Bain, a Weather Service meteorologist.

Urban areas like Houston, which was under a flood warning on Monday, are particularly prone to flooding because rain is poorly absorbed, if at all, in sprawling concrete communities, he said.

In last week’s storms, a low-pressure system from the west generated a mass of air that stayed moist and semitropical, setting off thunderstorms that moved across the southeastern and central parts of the state, Mr. Van Speybroeck said.

One of the hardest-hit places was Washington County, in southeastern Texas, an area of 622 square miles with a population of about 33,700.

John Brieden, the Washington County judge, who serves as a county administrator, said on Monday that workers were trying to assess the damage in the county, where 17 to 30 inches of rain had fallen in 24 hours by Friday.

“We are a rolling-hills area, so generally we don’t worry about flooding. It usually goes to low-lying areas,” Mr. Brieden said. “But this was so much water so quickly, so all of these streams and creeks were going over the tops of roads and bridges.”

The National Weather Service recorded 16.62 inches of rain in one day on Thursday in Brenham, the seat of Washington County, breaking a previous one-day record of 10.38 inches in 1994.

Outside Brenham, the body of a 21-year-old man, Darren Mitchell, was recovered after his truck was overtaken in a flood. KHOU television reported that he had posted a Facebook message saying, “And all I wanted to do was go home,” just before his family lost contact with him.

Mr. Brieden said he could not confirm that Mr. Mitchell had posted the message, which had an image of floodwaters lapping at the truck’s windows. Mr. Brieden said three other bodies had been retrieved from vehicles that had been carried off.

He said rescuers had carried out about 50 swift-water operations, sometimes with sonar, to search for people reported missing.

At least one bridge was washed out and approaches to others were inundated, making many areas of the county unreachable. More than 100 houses have been damaged, Mr. Brieden said.

“It is sprinkling right now,” he said around noon on Monday. “The rains haven’t gone away completely.”

And more rain is to come.

The National Weather Service has forecast eight to 10 inches and possibly up to a foot of rain from Wednesday through Friday in some central and southeastern parts of Texas.

“It’s a very small break in a pretty bad situation,” Mr. Van Speybroeck said. “The soils are saturated, and the rivers are swollen and flooded.”

In the central part of the state, Kirk C. Jenkins, a Kendall County warden, said the body of a 23-year-old woman had been retrieved on Sunday from a vehicle that became inundated by flash flooding near Comfort. Mr. Jenkins said it was his understanding that two other people in the vehicle were able to escape.

The storms also swamped Travis County, where rescuers in a helicopter retrieved the body of a man on Sunday during a search of a state highway area, said Lisa Block, a county spokeswoman. The man was not identified.

In Kansas, much of the central region was under a flash flood watch through the end of last week.

The Wichita Fire Department battalion chief, Scott Brown, was quoted in local news media as saying that rescuers planned to continue searching this week for an 11-year-old boy swept away on Friday by high, fast-moving waters in Gypsum Creek.

“We will work as hard as we can and as long as we can to try and bring some kind of closure and peace to the family,” Chief Brown told The Wichita Eagle.