The protest was organized and promoted by Women's March, the same group that mounted a massive protest effort previous year shortly after President Donald Trump took office. Kamala Harris, spoke.Protesters chanted slogans on their way to the Capitol, including, "No hate, no fear".
The "Families Belong Together" protests will include at least 16 in New Jersey, according to MoveOn.org, the liberal political action group that is one of dozens organizing the rallies.
It took 13 days to organize Saturday's demonstration against the Trump administration's "zero-tolerance" immigration policy and the detention of children and families.
According to reports, more than 500 people were arrested by the Capitol Police when they were having their sit-in protest at the Senate Hart Office building.
Thursday's protesters were joined by others around the country.
Several speakers, including Lin-Manuel Miranda, the creator of "Hamilton", and actors America Ferrera and Diane Guerrero, will take the stage at Lafayette Square to kick off the protest, which begins at 11 a.m. People who have lived through the Holocaust, Japanese internment camps and Trump's family separation policy are expected to speak.
The largest demonstration on Thursday saw the 90-ft atrium of the Senate Hart Office building overrun by hundreds of women who sat on the floor pumping their fists in the air.
Demanding the closure of the detention centers for illegal immigrants, the activists made a brief stop in front of the Department of Justice, urging the government to "abolish ICE", the Immigration and Customs Enforcement agency. They said people who were charged and fined could pay 24 hours after their arrests, but it was not clear who had been fined and how much.
"Since the beginning, President Trump has shown callous disregard toward mothers, fathers, and children who only want to find safety", Amnesty International USA's tactical campaigns manager Ashley Houghton said in a press release. Organizers of the D.C. rally also plan protests in 351 congressional districts around the country.