Citing government figures, The New York Times reported 17 people who were apprehended were part of families that crossed the border together while 18 people were considered "collateral apprehensions."
An unidentified Homeland Security official also confirmed to CNN that 35 people were arrested in the raids, which were slated to take place in Atlanta, Baltimore, Chicago, Denver, Houston, Los Angeles, Miami, New York and San Francisco. The Times previously reported the operation was aimed at apprehending families that recently crossed the border and which were notified in February to report to an Immigration and Customs Enforcement office and leave the United States.
Officials do not typically announce planned immigration raids ahead of time, according to The Associated Press. President Donald Trump, however, confirmed the raids were set to take place and touted the effort as a major operation in his efforts to stymie illegal immigration.
"If the word gets out, it gets out. Hundreds of people know about it," he told reporters July 12. "It's a major operation. … They're going to take people out and they're going to bring them back to their countries or they're going to take criminals out, put them in prison or put them in prison in the countries they came from."
The advanced notice spurred action from immigrant advocates and might have prompted some of those targeted to flee.
"There is no way to quantify the impact that had but you could turn on any TV station for several weeks (and learn about the raids), this being one of the lead topics," acting ICE Director Matt Albence told BuzzFeed News on Tuesday. "It's very difficult to locate those individuals who don't want to be found."
Albence told the Times on Monday that he was unaware of "any other population where people are telling them how to avoid arrest as a result of illegal activity."
"It certainly makes it harder for us to effectuate these orders issued," he said.
From mid-May to mid-July, nearly 900 people were arrested by ICE officers as part of cross-check operations in which regional field offices dedicate resources toward a goal like picking up people who remain in the U.S. despite final deportation orders or people suspected of entering the country illegally who have criminal records, according to BuzzFeed News.
White House officials on Tuesday said 605 people who have criminal records and who were suspected of entering the country illegally were recently picked up by ICE officers.