Nearly all of those killed in the storm drowned. Many have not yet been identified, including a 65-year-old man who was seen collapsing in floodwaters.

Six members of the Saldivar family — Belia and Manuel and their four great-grandchildren — Devy, 16; Dominic, 14; Xavier, 8; and Daisy, 6 — were found dead in a van, which was submerged in high water in east Houston.

Two people died because they could not get the necessary medical treatment, officials said.

There were those who braved the storm willingly, steering boats and cars through rising waters. Surviving family members said this week that their relatives were aware of the dangers of a storm that was bigger and more ferocious than any they had ever seen, but were overcome by a desire to help those who were imperiled.

Some victims lived alone and died solitary deaths. They called and texted loved ones with reassuring messages as the storm took hold, only to be found lifeless the next day.

In Galveston County, three men, aged 54, 59 and 83, were each found alone after the storm, drowned in their houses. Galveston attracts outdoorsy, headstrong, “loner-type folks,” said Erin Barnhart, the county medical examiner, noting that after days of searching, officials there have yet to locate the next of kin for one of the men.

“Presumably they were attempting to ride out the storm,” she said on Friday, adding that surviving previous hurricanes in Galveston could have left some residents feeling invincible. “They think they can handle it. They may have been a stubborn old man who said, ‘I’ve lived my life and if this is it, this is it.’”

A few of the victims died under unknown circumstances, leaving relatives and friends anguished over what they might have endured in their final hours.

Agnes Stanley, 89, a longtime volunteer for a conservation group in Houston, died in her one-story brick home there on Sunday. She was found floating in four feet of floodwater. “We don’t know what happened,” a son, Gregory Stanley, said.

Image Ruben Jordan told his son he was going to a sports bar to watch the fight. It was the last time the family heard from him. Credit... Clear Creek Independent School District

Roger Jordan, 35, heard from his 58-year-old father, Ruben Jordan, on Saturday evening, as the storm settled over Houston. “He had said he was going to go out to a sports bar and watch the fight,” he said, referring to the bout between Floyd Mayweather Jr. and Conor McGregor. Ruben Jordan, who had a long career as a high school teacher and football coach, went missing and drowned in the storm.

As Harvey raged this week, social media platforms quickly became clearinghouses for people looking for friends and relatives. Deborah Tucker of Baytown, Tex., posted on Facebook that her husband was missing. “His name is Mike Tucker, 66 yrs old, approx. 5’9,” she wrote. “I am very worried for his safety and appreciate any information.”

Later, an update appeared: “He has been found and didn’t make it. ThK u all for ur prayers. This is her daughter and she needs time before talking.”

While many in southeast Texas banded together to survive, there were others who died after venturing out to help others. Jorge Raul Perez, 33, and Yahir Rubio-Vizuet, 45, were killed in a boating accident while on a search-and-rescue mission in Harris County, their family said, adding that two men who joined them remain missing.

Sgt. Steve Perez, 60, a 34-year veteran of the Houston Police Department, drove in the dark for hours on Sunday morning while attempting to get to work; police said he had reached an underpass, had driven into the water and drowned.

Thelma Hooker, of Katy, Tex., said she was still trying to piece together the events of Wednesday, when her brother, Donald Rogers, called her to say that he and his wife, Rochelle, were busy checking on relatives, but would be home soon. They just needed to be satisfied, he told his sister, that everybody was all right.

“He didn’t come and I started getting worried,” Ms. Hooker said. Her phone soon rang with a frantic message, passed from a cousin to Ms. Hooker’s sister to her: There was a white truck in the raging water in nearby Fulshear, west of Houston, and it looked like their brother’s.

“The police officer said the current was so strong, it just wiped them off the bridge,” Ms. Hooker said, adding that she could not make sense of the situation. “My brother was a minister. He followed every rule.”

JoDell Pasek, of Houston, wept on Thursday as she described what had happened to her youngest son, Andrew, who was 25. An animal lover who once pulled over his car in San Antonio to rescue two abandoned puppies, Andrew was worried about his sister’s cat, D’Artagnan, left in her two-story house when she evacuated.

“He was a selfless person,” Ms. Pasek said. “He found out that they couldn’t take the cat with them, so he decided he was going to go over there.”

After parking his car, Andrew began wading through shallow floodwaters and was electrocuted, possibly by a live wire, according to Harris County officials.

Before he died, he shouted at a friend who had tagged along, Sean Stuart, not to touch him. “He knew immediately that if Sean touched him, he would be electrocuted too,” Ms. Pasek said.