The new crop is part of a trend. Nearly half of all House members were beginning their first, second, or third terms Tuesday.
In several cases they are replacing local fixtures: U.S. Reps. Jim Gerlach (R., Pa.), Allyson Y. Schwartz (D., Pa.), and Robert E. Andrews (D., N.J.) each had more than a decade in office before announcing retirements last year.
Locally, five of the nine members from Philadelphia and its immediate suburbs took office in 2011 or later.
For the three newcomers, Tuesday was steeped in ceremony. They brought spouses, parents, and children, and held open houses for supporters in their cramped new offices (freshmen pick last).
When Boyle, 37, inserted his newly acquired voting card on the House floor, he looked up to find his name lit up on the electronic board that tallies votes.
His wife, Jennifer; 1-year-old daughter, Abby; brother Kevin; and his father, Francis - an Irish immigrant - watched from the gallery. Kevin Boyle, a Pennsylvania state representative, surprised the family members by joining them after his drive to Harrisburg was stymied by snow.
"I can't imagine when Dad came to America 45 years ago, he was thinking he'd be here seeing his son sworn in the U.S. Congress," Boyle said, wearing his new congressional lapel pin, marked "114" for the 114th Congress.
"It is pretty amazing that what our founding fathers started almost a quarter of a millennium ago in Philadelphia is basically, with little change, the same thing that we were just continuing here today," Boyle said.
At his desk with his wife, Christine, early Tuesday, Costello, 38, had a stack of business cards, an open can of lemonade, and a photo of his 1-year-old son, Ryan Jr.
On the walls, freshly painted baby blue, were old photographs of former President Lyndon B. Johnson and former Vice President Dick Cheney, who each began their congressional careers in the same office. Sliced bagels awaited guests coming later.
"When I walked into the Cannon Office Building yesterday, it was definitely a different mental approach," Costello said. "The wrapping paper is off and realism has sort of set in."
Costello will represent a district based in Chester County.
A busload of supporters and dozens of family members and friends came to greet MacArthur at his new office, overlooking the scaffolded Capitol dome. The walls of his office were bare, aside from a framed replica of the Constitution.
MacArthur's wife, Debbie, described the feeling of pride as she watched him cast his first vote, for John Boehner as speaker of the House. His children, David and Isabella, and father were also there.
MacArthur, whose district includes much of Burlington and Ocean Counties, said he hopes to quickly turn to building relationships to pass bills. As priorities he named veterans affairs, advocating for South Jersey's McGuire-Dix-Lakehurst joint military base, and job creation.
"These are the things that made me run and those are the things I want to get started with," said MacArthur, 54.
Costello said he hopes to ease some regulations on businesses included in the Affordable Care Act - including repealing a tax on medical device makers.
He will also work on the committees that handle veterans affairs and transportation, and said he hoped to have a role in education policy.
With so many relatively new members in Congress, Costello said, he sees "an opportunity."
"In certain subject matter areas, if I put my nose to the grindstone and really focus and be thoughtful," Costello said, "I can be somebody who has an outsize role relative to being a freshman member."
Boyle said he hopes to team with Costello or other local Republicans to craft a transportation funding bill that could provide an economic spark to the Philadelphia region.
He also said he hopes to boost constituent services in his Philadelphia and Montgomery County district by doubling the number of local offices to four.
Other local officials also began new chapters.
U.S. Sen. Cory A. Booker (D., N.J.) was sworn in to his first full term. He has been in office since 2013, filling the unexpired term of the late Sen. Frank R. Lautenberg.
Booker pledged to focus on the economy - he pointed to funding for infrastructure projects and reducing corporate tax rates - and to continue pressing for changes in the criminal sentencing system.
U.S. Rep. Patrick Meehan (R., Pa.) of Delaware County will join the influential Ways and Means Committee.
Bucks County Rep. Mike Fitzpatrick (R., Pa.) began what he has said will be his fourth - and last term - in Congress.
Pennsylvania's 18-person House delegation, with Schwartz's departure, is now all-male.
New Jersey added a woman to its previously all-male 12-person House delegation: Mercer County Democrat Bonnie Watson-Coleman.
All members of the House took their oaths together on the House floor, before moving on to receptions and ceremonial swearing-ins where they could pose for pictures with their families.
"Today is going to come and go," Costello said, "and the serious work of why I ran is going to front and center, and I've been waiting for that."