Migrants now face new restrictions on entry, and will not be allowed in if they arrive at the border without first applying online or seeking asylum in a country they passed through to reach the US.
The US has reported a sharp fall in migrant "encounters" at its border with Mexico after COVID-era Title 42 restrictions ended last week.
Title 42 allowed US authorities to quickly send migrants back to Mexico without the chance of requesting asylum. It was intended to stem the spread of the coronavirus.
The health order was enacted by then-president Donald Trump and expired on 11 May.
Migrant "encounters" have fallen 70% since the restrictions ended, Homeland Security official Blas Nunez-Neto said.
An encounter refers to when US officials encounter non-US citizens attempting to cross the border into the US from Mexico without authorisation.
Mr Nunez-Neto said the numbers illegally entering the US had continued to tick down after an average of 4,000 encounters a day, as of 12 May.
"In the last 48 hours there were 3,000 encounters a day on the border, this is a more than 70% reduction," he said on Friday.
He added that about 11,000 people were removed from the US in the last week and sent to more than 30 countries.
That figure included more than 1,100 people from Venezuela, Nicaragua, Haiti and Cuba who were returned to Mexico.
Migrants entering US face new restrictions
Thousands of migrants crossed into the US in the week before the regulation expired.
Migrants now face new restrictions on entry.
They will not be allowed in if they arrive at the border without first applying online or seeking asylum in a country they passed through to reach the US.
Anyone caught crossing the border illegally will not be allowed to return to the US for five years. They will face criminal prosecution if they do.
Human rights groups have criticised the new rules, saying they wrongly assume safety for migrants in countries outside the US, adding that the online application system has proven unworkable for the vast majority.