When the private data from the 1950 Census was finally unveiled early Friday, David Ferriero, the head of the National Archives, logged onto the Archives website to search for his family.

He found Beverly, Mass., the coastal town north of Boston where he grew up, and the address on Walnut Avenue, where he had lived.

And there, listed as head of the household, was his father, Anthony P. Ferriero, then 40, an auto mechanic who the Census said had worked 64 hours the previous week at a local garage.

David Ferriero, the head of the National Archives, searched for his family Friday in the Archives census data. He was 4 in 1950. (David Ferriero)

There, too, were his mother, Marie, 32, his brother, Anthony C., 11, his sisters, Marie A., 9, and Kathleen, 2, and four-year old David, himself, who is now 76. It was the first Census in which he appeared, he said in a blog post Friday.

Ferriero was among thousands of Americans who began searching the 6.4 million digitized pages of personal 1950 Census records released by the Archives at 12:01 a.m. Friday.

The data, which had been kept secret to protect privacy for 72 years, was a trove for genealogists.

“I haven’t gone to sleep yet,” Stephen P. Morse, an amateur genealogist and computer expert in San Francisco, said Friday afternoon. “I’ve been up all night.”

On Saturday, April 1, 1950, an army of 140,000 census enumerators had started out across the country to interview the roughly 151 million residents in 46 million households.

The data they collected includes names, ages, addresses and answers to questions they asked about employment status, job description and income.

Women were asked, if married, how many children they had borne. People were asked where they worked, where their parents were born, how much money they made and how much money relatives in the home made.

Next door to the Ferrieros on Walnut Avenue, were the Gardners, Norman, 43, his wife, Norma, 46, and their son, David, 16. Norman was a meter technician in a shoe machine factory, the Census enumerator reported.

Elsewhere on Walnut Avenue were Gertrude Shattuck, 39, a secretary for a car insurance firm, Charles H. Perkins, 63, an order clerk at a factory, and Oswald Evitts, 64, a machinist at a power plant.

They were all part of the giant national snapshot.

And along with Ferriero, an estimated 26 million Americans living in the country in 1950 are still alive.

Morse, the genealogist, said he found his family in the data at about 3 a.m. Friday. They were in a second-floor rear apartment at 85 Newport Street in the Brownsville section of Brooklyn. His father, Morris, was an accountant.

“I really wanted to find this because it’s the only census where my entire family, the whole grouping, is together,” he said. “My mother, my father, my sister, myself and my grandmother.”

“It was exciting,” he said. “A nice thing to put into my genealogy scrap book.”

Now 81, he was 9 when the enumerator visited in 1950.

The 1950 Census was the nation’s 17th. It has been conducted every 10 years since 1790, by order of the Constitution.

Enumerators were sent to visit people wherever they lived or were staying — homes, apartments, hotels, Indian reservations, boats, tents and railroad cars.

Native Americans on reservations were asked on a separate form if they were “full blood, half to full, quarter to half, less than ¼.” They were also asked if in 1949 they had participated in or attended “any native Indian ceremonies.”

“What many people don’t know is that the census is particularly important to Indian tribes,” Interior Secretary Deb Haaland, member of the Pueblo of Laguna tribe, said in one of the prerecorded announcements that helped launch the release.

“Because it helps decide federal funding, which then impacts the government’s responsibility to native communities,” she said.

Alvin Thornton, 73, of Upper Marlboro, Maryland, with his daughters, Kenya and Octavia, born in 1972 and 1977. (Alvin Thornton)

Alvin Thornton, 73, of Upper Marlboro, Md., had seen the 1870 Census, which recorded his great-grandparents, who were born into slavery.

He found his grandmother and his mother and father in later surveys. But Friday was the first day that Thornton, a professor emeritus and former chair of the political science department at Howard University, was able to search for himself.

On April 1, 1950, he was 1-and-a-half, the youngest of seven children living in a four-room wooden house in Rock Mills, Alabama.

“A typical, rural, what we call a sharecropper’s home,” he said of the structure, which was owned by a white landlord who also owned the land and equipment his father used to grow cotton. “The home would certainly have had no inside running water, no inside toilets, or anything like that.”

Three years later, when his father got a job at a cotton mill, his family moved, and in 1971 Thornton moved to the Washington area.

On Friday, he was online, looking for the form that would have listed himself and his older siblings (three more were born who won’t appear until the 1960 Census), along with his wife. “I started searching, and my search engine is not picking me up right now,” he said.

Eventually, he said, he found himself and his family in the records.

Hamil R. Harris contributed to this report.