The U.S. runners finished in 3 minutes, 16.87 seconds to nab the country's fifth consecutive Olympic title in the event. Russia finished second in 3:20.23, and Jamaica was third in 3:20.95. The United States' 3.36-second margin was the largest in the final of the long relay at the Olympics since East Germany beat the United States by 3.58 seconds in 1976.
Allyson Felix, who won her third gold medal of the Games, gave the United States a 20-meter lead after the second leg, then delivered the baton to Richards-Ross, who was basically running alone as she breezed across the finish line.
"By the time I got the stick," Richards-Ross said, "it was basically a victory lap."
DeeDee Trotter ran the opening leg for the United States and built a lead before handing off to Felix, who more than doubled the advantage by the time she passed to Francena McCorory.
"The ladies were phenomenal," Richards-Ross said. "They made it too easy for me."
Richards-Ross already had won a gold medal in the 400-meter race. Her husband traveled to London to watch her in that race.
The 27-year-old Richards-Ross, a native of Jamaica, has dual citizenship. Her parents moved to the United States when she was 12, in part because of better training opportunities.
Richards-Ross has fought on and off the last five years with a hard-to-diagnose illness that causes fatigue and skin lesions. She fought with her own emotions after a disappointing bronze medal in the 400 in 2008.
No real stress this time, though, and the U.S. women hardly looked winded as they danced and circled the track with American flags held high behind their heads.
The Associated Press contributed to this report.