Johnson disclosed the beefed-up federal presence during a sometimes-acrimonious congressional hearing in which Republicans blamed a 2012 decision to slow the deportation of immigrants brought the country illegally as children for sparking a surge in minors crossing the border.
House Committee on Homeland Security Chairman Rep. Mike McCaul (R-Texas) told Johnson that the U.S. needs to send a message that "if you come, you can't stay."
The number of children entering illegally has more than doubled since last year, federal statistics show.
Families from El Salvador, Guatemala and Honduras pay smugglers thousands of dollars to bring children to the U.S.
Johnson said that investigators last month arrested 163 alleged members of smuggling rings operating in El Paso, Houston, San Antonio, Phoenix and San Diego.
"I think the key is the money trail," Johnson said. "The money trail starts in the U.S., and if we can track the money, we go a long way toward solving this problem."
Administration officials attribute the increase to rising violence in Central American cities and to false rumors about legal residency permits being awarded to children who reach the United States.
Johnson said that he is considering "every conceivable lawful option to address this situation."
McCaul urged the Obama administration to deploy National Guard soldiers to help stem the flow of children.
National Guard troops have helped monitor surveillance cameras, fly aircraft, build fences and man observation posts along the Southwest border. But the Pentagon has resisted activating more National Guard members because there isn't a clear mission for them in this case, officials said.
"Having the Guard on the border has some limitations," Border Patrol Deputy Chief Ronald D. Vitiello told the panel. "This work is best done by law enforcement agents."
Vitello emphasized that it is "not a challenge to arrest" children and parents crossing with children. Most are surrendering themselves to Border Patrol agents.
By law, Customs and Border Protection must deliver unaccompanied minors to shelters run by the Department of Health and Human Services within three days. But with so many children now in custody, the
The Obama administration has created temporary camps at Border Patrol stations, as well as at Lackland Airforce Base in San Antonio and at Naval Base Ventura County in Port Hueneme.
Dormitories at a federal law enforcement training center in Artesia, N.M., are also being prepared for parents caught entering the country with children.
"It's a much better life than they're getting right now in Central America, so I don't know how that's going to in any way stall what's happening," King said.
The practice of uniting children found alone on the border with relatives in the U.S. undermines the message that migrants who cross the border illegally can't stay, Republicans said.
Johnson confirmed that more than half of the unaccompanied minors from Central America were turned over last year to family members in the U.S. while deportation orders were under review.