Trump announces that former ICE director Tom Homan will join the administration as “border czar.”

Former Immigration and Customs Enforcement Director Tom Homan will be the “border czar” in the Trump administration, President-elect Donald Trump announced on Truth Social.

Homan, a staunch Trump supporter, will be responsible for the mass deportations Trump promised during his 2024 campaign.

“I have known Tom for a long time, and there is no one better at monitoring and controlling our borders,” Trump wrote in his post Sunday evening.

“Similarly, Tom Homan will be responsible for all deportations of illegal aliens back to their country of origin. Congratulations to Tom. “I have no doubt that he will do a fantastic and long-awaited job,” Trump added.

Homan oversaw ICE during the Trump administration's “zero tolerance” enforcement, which separated parents from their children at the border.

The American Civil Liberties Union (ACLU) estimates that there are between 500 and 1,000 families who have not been reunited.

In August, ACLU attorney Lee Gelernt told ABC News it was impossible to know an exact number because they hadn't found everyone.

In an interview with “60 Minutes” in October, Homan said future family separations would need to be considered, but also said, “Families can be deported together.”

With immigration a top issue for voters, Trump has said he is committed to detaining and deporting millions of migrants living in the United States without legal permission.

During his rally at Madison Square Garden in New York City in October, he reiterated his campaign promise to carry out mass deportations on “Day 1.”

“On day one, I will launch the largest deportation program in American history to get the criminals out,” he said. “I will save every town and village that has been invaded and conquered, and we will put these vicious and bloodthirsty criminals in prison and then drive them out of our land as quickly as possible.”

To accomplish this, the former president said he would use local law enforcement and the National Guard to find migrants living anywhere in the United States

Trump has railed against the Biden administration's immigration policies, claiming in part that they have made America less safe, even though statistics show that U.S.-born citizens are more than twice as likely to be arrested for violent crimes as undocumented immigrants.

An estimated 11 million people live in this country without legal immigration status.

According to a report from the American Immigration Council, the cost of deporting even 1 million undocumented immigrants per year, if feasible, would be over $88 billion, for a total of $967.9 billion over a period of more than 10 years.

ABC News' Armando Tonatiuh Torres-García and Meredith Deliso contributed to this report.