Jonathan Cilley (July 2, 1802 - February 24, 1838) was a member of the U.S. House of Representatives from Maine. He served part of one term in the 25th Congress. He died in office after being killed in a duel by Congressman William J. Graves, a colleague from Kentucky.
Jonathan Cilley was a member of one of the leading families of northern New England. A grandson of Major General Joseph Cilley, he was born in Nottingham, New Hampshire, and graduated from Bowdoin College in 1825. Deciding to stay in Maine, he studied law and was admitted to the bar in 1828, practicing in Thomaston, Maine. He represented Thomaston in the Maine Legislature in 1831-1836, serving as speaker of the state House in his final two years of service there. He was then elected to Congress, but did not complete his first term.
Jonathan Cilley's brother Joseph Cilley served briefly as a U.S. Senator from New Hampshire in 1846-1847. Jonathan Cilley's successor as speaker of the Maine House in 1837 was Hannibal Hamlin, afterwards U.S. vice president.