DILLEY, Tex. — Jeh C. Johnson, the secretary of Homeland Security, came to this South Texas outpost on Monday to open the country’s largest immigration detention facility and draw attention to border security measures that are part of President Obama’s fiercely debated executive actions on immigration.

While Mr. Obama has offered protection from deportation and work permits to millions of unauthorized immigrants, he has also ordered efforts to reinforce the southwest border to prevent a new surge of illegal immigration. The 50-acre center in Dilley, 85 miles northeast of Laredo, will hold up to 2,400 migrants who have illegally crossed the border and is especially designed to hold women and their children.

Standing on a dirt road lined with cabins in a barren compound enclosed by fencing, Mr. Johnson delivered a blunt message to families without legal papers considering a trip to the United States: “It will now be more likely that you will be detained and sent back.”

Republicans have assailed Mr. Obama’s measures, saying he overstepped his constitutional authority with a sweeping program of deportation reprieves that they predict will attract another wave of migrants like the one in Texas’ Rio Grande Valley this summer.