The Willners are flabbergasted by the support - and heartened.
"Regardless of political party, so many of us are distraught over children being separated from their parents at the border," Charlotte Willner said. "We can't all be on the front lines to help these families, but by supporting Raices, we're able to do something that just takes less than a minute, and collectively have an impact."
According to the Willners, the average donation is just US$40. Private donors have also matched the first US$250,000. A well-placed post in Pantsuit Nation, an online platform that organises activists, gave the fundraiser its boost toward a million.
Raices, which has headquarters in San Antonio, has been on the front lines of the immigration battle for a long time. Its education, outreach and development director Jenny Hixon said that although the zero-tolerance border-crossing policy began in April, the detention centres and cage structures coming out in news stories now have actually been around years.
"We've all talked among ourselves [at Raices] that if people knew what was happening, they would be horrified," Hixon said. "The system isn't set up for kindness, compassion or justice. Now that people know and people see, if they keep the pressure up, there is really a chance that we can change this."
Nearly 2000 children were separated from their adult guardians at the border between April 19 and the end of May, according to the Department of Homeland Security.
When children are separated from their parents, Hixon explained, the parents are usually taken to a detention centre to await a trial.
Unable to raise money for bail, they can wait for months, or even years, she said. If or when they do get out, many times their children are no longer where they can find them.
"The sheer panic a parent must feel, I can't imagine," she said. "Last year, our family detention programme served 7000. It's a small and scrappy team of folks that do amazing work. When we committed to the bond programme we jumped because we thought it was really important. We jumped and the US citizens caught us."
Raices funnels resources to these parents in the form of bond payments and free or low-cost legal representation for them and their children. More than 13,000 children went without representation last year, and bonds can be in the tens of thousands. The typical bond is US$1500, which is why the Willners chose that as a goal.
"We originally set it up to raise US$1500, and clearly there's a lot of public enthusiasm to help these families," Willner said.
"We don't think we're a meaningful part of this compared to the overwhelming tide of support from everyone who has given. Donating is the easy part, so our hope is that people continue to be hungry for information and get involved."
With the millions pouring in, RAICES has gone into overdrive to beef up relief efforts, hire more qualified lawyers and professionals, and fulfill more of their pie-in-the-sky initiatives than they ever thought would be possible.
"This is one of those cases where we can now do things we've always wished we could do," thanks to donations, Hixon said.
"We're ramping up our representation of the parents. We're hiring more legal point people who try to get the families back in communication with each other. We're launching a nationwide network of people to provide support to people after they are released from detention, because as you can see, this is traumatising."
Often the children need help when they leave detention. Their family has been altered and they may suffer PTSD, separation anxiety, toxic stress and more. The detainment will have long-term effects so Raices is setting up a network of therapists and psychologists to help.
Raices will get the money from the Facebook fundraiser by mid-July, when Facebook releases the funds raised the previous month through its donations services. Facebook and the Willners take nothing; 100 per cent of the donations go to the organisation.
As for the Willners, who met in Silicon Valley working in the tech industry, they say they're happy to have been able to help.
"When we all come together in community efforts like this," Charlotte Willner said, "we can find an antidote to the feelings of helplessness."
