"This is the dream that Dr. King talked about in his speech. We see history in the making," said Joyce Oliver, who observed King Day by visiting the National Civil Rights Museum in Memphis, Tenn., built on the site of the old Lorraine Motel, where King was assassinated in 1968.
In Atlanta, at the 45th annual service for the civil rights leader at the church where he was pastor, those gathered in the sanctuary were invited to stay to watch President Barack Obama's second inauguration on a big-screen TV.
As the nearly three-hour service came to a close at Ebenezer Baptist Church, organizers suggested forgoing the traditional singing of "We Shall Overcome" because the inauguration was about to begin. But the crowd shouted protests, so the choir and congregation sang the civil rights anthem before settling in to watch the events in Washington.
In the nation's capital, several dozen people took turns taking pictures of the King statue before heading to the National Mall, about a 15-minute walk away, for the inauguration.
Nicole Hailey, 34, drove in with her family from Monroe, N.C., a six-hour trip that started at midnight. She attended Obama's first inauguration four years ago and was carrying her Metro ticket from that day, a commemorative one with the president's face printed on it.
She and her family visited the King memorial before staking out a spot for the swearing-in.
"It's Martin Luther King's special day," she said. "We're just celebrating freedom."
At the ceremonial inauguration, Obama took the oath using a Bible that had been owned by King. He called it "a great privilege." The King Bible was one of two used; the other had belonged to President Abraham Lincoln.
In Columbia, S.C., civil rights leaders paused during their annual King Day rally to watch the inauguration on a big screen. Most of the crowd of several hundred stayed to watch Obama's address.
"You feel like anything is possible," Jelin Cunningham, a 15-year-old black girl, said of Obama's presidency. "I've learned words alone can't hurt or stop you, because there have been so many hateful things said about him over the past four years."
At the Atlanta service, King's youngest daughter, Bernice King, said the country had been through a difficult year, with divisive elections, military conflicts and natural disasters.
"We pray that this day will be the beginning of a new day in America," she said. "It will be a day when people draw inspiration from the life and legacy of Martin Luther King Jr. It will be a day when people realize and recognize that if it were not for Dr. King and those who fought the fight fought in that movement, we would not be celebrating this presidency."
She also stressed her father's commitment to nonviolence, saying that after the 1956 bombing of the family's home in Montgomery, Ala., her father stood on the porch and urged an angry, armed crowd to fight not with guns but with Christian love.
"This apostle of nonviolence perhaps introduced one of the bravest experiences of gun control that we've ever heard of in the history of our nation," she said.
The service also kicked off a year of celebrations of the 50th anniversary of King's "I Have a Dream" speech, delivered Aug. 28, 1963, in Washington. A group of students, led by King's great-niece Farris Christine Watkins, delivered sections of the speech in turn.
By the end, the crowd was on its feet, shouting, "Free at last! Free at last! Thank God Almighty, we are free at last!"
The keynote speaker was the Rev. Samuel Rodriguez, president of the National Hispanic Christian Leadership Conference, a socially conservative evangelical association. It marked the first time a Latino had been invited to deliver the King Day address at Ebenezer Baptist.
He urged the audience to work to fulfill King's dream.
"Silence is not an option when 30 million of our brothers and sisters live in poverty," he said. "Silence is not an option when 11 million undocumented individuals continue to live in the shadows."