Interest in the newly released US census of 1940 was so great that the government website was nearly paralysed shortly after the records became available.
Computer experts were working on the site to bring it up to speed as soon as possible. Cooper did not give an exact time when the site would be fully operational.
"We're adding a lot more servers, a lot more muscle to the website," she said.
More than 21 million people still alive in the US and Puerto Rico were counted in the 1940 census. The census followed a decade when tens of millions of people in the U.S. experienced mass unemployment and social upheaval as the nation clawed its way out of the Great Depression and rumblings of global war were heard from abroad.
Monday's release includes digitized records for details on 132 million people. Access to the records is free and open to anyone online, but they are not yet searchable by name.
For now, researchers will need an address to determine a census enumeration district - a way to carve up the map for surveying - to identify where someone lived and then browse the records.
Every decade since 1942, the National Archives has made available records from past censuses. The records, which include names, addresses and income and employment information, are rich with long-veiled personal details.