One of the largest of Sunday's protests took place at Battery Park in lower Manhattan, within sight of the Statue of Liberty in New York Harbor, long a symbol of welcome to U.S. shores.
Democratic Senator Charles Schumer of New York told the crowd that the Trump order was un-American and ran counter to the country's core values.
The march, estimated to have grown to about 10,000 people, later began heading to the U.S. Customs and Border Protection office in lower Manhattan.
Organizers estimated that more than 10,000 people gathered at Boston's Copley Square to demonstrate against Trump's executive order.
next slide will load in 15 secondsSkip AdSkip AdSpeakers in Boston included Senator Elizabeth Warren of Massachusetts, a vocal critic of Trump and a leader of the Democratic Party's liberal wing.
During the protests, dozens of Muslims, some of them kneeling on protest signs, bowed in prayer on rugs laid out grassy patch of ground in the square.
In Washington, thousands rallied at Lafayette Square across from the White House, chanting: "No hate, no fear, refugees are welcome here."
As the crowd passed the Canadian Embassy en route to the Capitol, protesters chanted: "Hey hey, ho ho, I wish our leader was Trudeau."
The chant was a reference to Canadian Prime Minister Justin Trudeau's Twitter message on Saturday reaffirming his country's welcoming policy toward refugees. He was one of many global leaders who criticized Trump's order.
next slide will load in 15 secondsSkip AdSkip AdProtesters marched along Pennsylvania Avenue, stopping at the Trump International Hotel where they shouted: "Shame, shame, shame."
A crowd estimated by police at 8,000 eventually arrived at the steps of the U.S. Capitol, where a line of uniformed officers stood guard.
Hundreds of protesters gathered at Los Angeles International Airport (shown here), Dulles International Airport, and New York's John F. Kennedy International Airport, among others.
A massive crowd formed at the international arrivals gate of the Dallas/Fort Worth International Airport in Texas.
Anxious families awaited relatives detained for hours at JFK and other airports after flights from countries affected by the presidential order.
next slide will load in 15 secondsSkip AdSkip AdPeople gathered to pray in baggage claim at the Dallas/Fort Worth International Airport.
Federal judges issued rulings on Saturday and Sunday preventing the deportation of affected travelers stuck in airports across the US, but the long-term effects and legality of the executive order remain unclear.
Sens. John McCain of Arizona and Lindsey Graham of South Carolina became two of the most prominent GOP lawmakers to criticize the ban, saying they "fear this executive order will become a self-inflicted wound in the fight against terrorism."