About 2,000 people endured a downpour in Atlanta to hear speakers talk of the need for justice for Trayvon Martin and other black youths.
The Trayvon Martin Prayer Vigil and Rally, in downtown, began with chants of "no justice, no peace," and "Trayvon, Trayvon, Trayvon" before speakers urged the crowd to register to vote and to seek repeal of Georgia's stand your ground law.
Martin Luther King III urged the audience to go to Washington, D.C., on August 24 for the 50th anniversary of the March on Washington and his father's famous "I Have a Dream" speech. "It's marching time, ladies and gentlemen," he said.
At least several people in the crowd were treated for heat-related illness after fainting on the sweltering day.
At a rally in Miami, Martin's father, Tracy, told supporters that after the acquittal he has "come to realize George Zimmerman wasn't on trial - Trayvon was on trial."
In Los Angeles, about 500 people converged on the federal courthouse in Los Angeles under gray skies, toting signs saying "Open Season on the Black Man" and "This Should Not Be OK in 2013 America."
In Chicago, some 500 people rallied across from the Everett McKinley Dirksen federal courthouse.
"We are standing up here today to say to our young people, 'we value your lives,'" said Chicago Urban League Chief Executive Officer Andrea Zopp, who has a 17-year-old son. "The civil rights movement is not over."
Rapper MC Lyte told the crowd: "When the verdict was read, I felt like we lost Trayvon Martin all over again."
In Oakland, a crowd of up to 150 people demonstrated peacefully in the city's downtown, occasionally singing "We Shall Overcome" before dispersing in the late afternoon.
And across the bay in San Francisco, about 100 people gathered in front of the Federal Building.
Reverend Arnold Townsend, 70, vice president of the local NAACP chapter, vowed to "bring to light this incident (and) let black children know the system has them under attack."