Sarah Kelly Elfreth (/ˈɛlfrəθ/, ELF-rəth; born September 9, 1988) is an American politician who is serving as the U.S. representative for Maryland's 3rd congressional district since 2025. A member of the Democratic Party, she represented the 30th district in the Maryland Senate from 2019 to 2025.

Born and raised in New Jersey, Elfreth moved to Maryland to study political science at Towson University and later earn a MPP from Johns Hopkins University. She became involved with Maryland politics while attending Towson, during which she was appointed by Governor Martin O'Malley to be a student member of the University System of Maryland Board of Regents. After graduating, Elfreth moved to Annapolis, where she successfully ran for the Maryland Senate in 2018, defeating Republican challenger and former state delegate Ron George in the general election. She was reelected in 2022. Her district encompassed the lower half of Anne Arundel County, including the state capital of Annapolis.

Elfreth won the 22-way Democratic primary in the U.S. House of Representatives election in Maryland's 3rd congressional district and then defeated the Republican nominee in the general election. She was sworn in on January 3, 2025.

Elfreth was born and raised in Barrington, New Jersey, where her stepfather worked as a locomotive engineer and her mother worked as a probation officer. Her grandfather served in the Korean and Vietnam wars, and later suffered from post-traumatic stress disorder. She is of English descent and is a descendant of Jeremiah Elfreth, who was the namesake of Elfreth's Alley in Philadelphia.

Elfreth graduated from Haddon Heights High School in 2006, and attended Towson University on scholarship, where she served as a resident assistant, submitted a thesis on how having students participate in governing boards can make them more effective, and received a Bachelor of Arts degree in political science in 2010. In 2012, she earned her Master of Science degree in public policy from Johns Hopkins University, where she worked as a research assistant in the Office of Government and Community Affairs from 2010 to 2012. Since 2019, Elfreth has taught as an adjunct professor for Towson University's Honors College.

Elfreth became active in politics while attending Towson University, when she became involved with student government and began traveling to Annapolis to lobby the Maryland General Assembly. She also worked as a summer intern for state senator James Rosapepe. In 2009, Maryland governor Martin O'Malley appointed Elfreth to be the student member of the University System Board of Regents. She didn't become involved with electoral politics until her senior year at Towson, after hearing a speech by former Vermont Governor Madeleine Kunin. She served as a congressional intern for House Minority Whip Steny Hoyer in 2011 before working as a lobbyist for the National Aquarium and Johns Hopkins University. After moving to Annapolis, Elfreth became involved with local politics, becoming a member of the Ward 1 Residents Association and serving on the District 30 Democratic Club, and volunteering for the campaigns of multiple local Democratic officials. Before running for the Maryland Senate, she worked as a senior director for Margrave Strategies, a consulting firm founded by former Howard County Executive Kenneth Ulman.

In June 2017, Elfreth filed to run for Maryland Senate, seeking to succeed state senator John Astle, who did not seek re-election to run for mayor of Annapolis. During the Democratic primary, she ran on a slate with House Speaker Michael E. Busch, whom she would later cite as her political mentor. Elfreth was elected to the Maryland Senate with 53.8 percent of the vote against former state delegate Ron George.

Elfreth was sworn into the Maryland Senate on January 9, 2019. As of 2024, she is the youngest woman ever to serve in the Maryland Senate. Elfreth was a member of the Budget and Taxation Committee—including as the chair of its Pensions and Public Safety, Transportation, and Environment subcommittee and as a member of its Capital Budget subcommittee—and was the chair of the Joint Committee on the Chesapeake and Atlantic Coastal Bay Critical Areas and Joint Subcommittee on Program Open Space and Agricultural Land Preservation. She was regarded as one of the most productive members of the legislature, having passed 84 bills during her tenure, more than any other legislator during that time.