Philadelphia ? Who lived in your neighborhood 72 years ago? What was your grandparents’ house worth? Did they have one of those gadgets called a radio?

As if unlocking an antique national file cabinet, the U.S. Census Bureau on Monday will release 122,288,177 original, confidential records from the 1930 census a gold mine for genealogists, family-history buffs and busybodies of all kinds.

Genealogists, who already have census records from 1920 and earlier, hope to learn what transpired in their families and hometowns through the Roaring Twenties, that post-World War I decade that started with the invention of the Band-Aid and ended with the stock market crash.

“This is so exciting,” said Sylvia Wilkins, 45, a financial manager and South Philadelphia native who has tracked her roots in several censuses. “I think I know more about my family from looking at the census than I ever would’ve been told by family members.”

Under federal law, personal details compiled in each decennial census must be released after 72 years. (Congress set the time period to protect privacy back in 1952, when the average life span was 68 years. Today, it’s 76.)

Each 30-question form, which most census-takers had filled out by hand, contains information by name and address for a person’s “marital condition,” “whether able to read and write,” and on the cusp of the Great Depression whether “actually at work yesterday.”

People were asked what year they immigrated, where they were born, and what language they spoke “at home before coming to the United States.”

It was a few years after Congress imposed the first major numerical limit on immigration, and it was the last time the census put the foreign-born population higher than 10 percent until 2000.

The census asked for “color or race.” Census-takers were instructed to write “white” in cases of mixed heritage if “the person is regarded as white in the community,” according to genealogist Kathleen Hinckley.

Potential surprises

And seven decades later, original census forms have been known to reveal that a person’s race was different than his or her descendants thought.

Wilkins said there can be other surprises. When researching relatives in the 1920 census, she discovered certain family members had been boarders, not owners of their Philadelphia home. Other relatives changed careers between censuses.

Questions have changed slightly each decade. The new query in 1930 was whether a home had a “radio set,” comparable to efforts today to count homes with Internet access.

A year later, RCA Victor, which had just started making radios at a modern plant in Camden, was accused by the government of monopolizing the market.

And within three years, radios would be the primary method of mass communication for two world leaders, Franklin D. Roosevelt and Adolf Hitler.

In 1930, Pennsylvania was the second-most-populous state after New York, and New Jersey was 10th. Philadelphia, with 1.95 million people, was the third-biggest city behind New York and Chicago.

Two-thirds of the region’s 3.1 million people lived inside the city, the reverse of the distribution of its 5.1 million people today.

In striking similarity to today’s annoyance at telemarketers, Philadelphia census-taker John Yerkes told The Philadelphia Inquirer in April 1930 that he interviewed people in the evening because they “often refuse to answer doorbells in the daytime, because they think it’s a peddler.”

A gold mine

The Genealogical Society of Pennsylvania, which is having seminars on the archives, believes this is the “largest release of genealogical data in history,” said James Beidler, executive director.

Beidler noted a 72-year waiting period may have been sufficient a half-century ago, but today many people live longer and will be able to find information about themselves as children through a census-taker’s eyes.

“You read all kinds of handwriting, all kinds of interpretations of people they met,” Wilkins said.

Forms for the whole country, on microfilm, will be released at each of 14 National Archives offices across the country, including its Mid-Atlantic facility in Center City. Some companies and groups plan eventually to put a searchable index on the Internet.