Homeland Security said it detained 46,195 people in October, up from 39,501 in September and 37,048 in August.
The number of migrants illegally entering the United States from Mexico jumped more than 16 percent in October, US officials said on Thursday.
The US Department of Homeland Security said it detained 46,195 people in October, up from 39,501 in September and 37,048 in August.
"There are currently about 41,000 individuals in our immigration detention facilities -- typically, the number in immigration detention fluctuates between 31,000 and 34,000," DHS Secretary Jeh Johnson said in a statement.
"I have authorized US Immigration and Customs Enforcement to acquire additional detention space for single adults so that those apprehended at the border can be returned to their home countries as soon as possible," he said.
Immigration officials have said that most of the undocumented arrivals are actually Central Americans making the arduous journey through Mexico to seek work and safety in the United States -- amid poverty and a surge in gang-related violence at home.
US officials have "engaged with a number of countries to repatriate their citizens more quickly, and they have agreed to do so," Johnson said, noting that many of the new arrivals have been asylum seekers and young children.
"Our borders cannot be open to illegal migration. We must, therefore, enforce the immigration laws consistent with our priorities," he added.
"We prioritize the deportation of undocumented immigrants who are convicted of serious crimes and those apprehended at the border attempting to enter the country illegally."
The latest immigration figures come two days after the November 8 presidential election that closed a campaign in which immigration has loomed large.
The immigration issue has been central in the candidacy of Republican President-elect Donald Trump, who has vowed to build a wall along the southwestern border and make Mexico pay for it.
Trump met for an hour Thursday with the head of the US Senate Mitch McConnell, and again stressed his plans to highlight immigration during his presidency which starts in January
"We're going to look very strongly at immigration," the billionaire businessman said.