Nellie Mathes Horne (May 26, 1870 – May 26, 1950) was an American painter. Born in Eliot, Maine, Horne was the daughter of John Harrison and Lizzie N. (Young) Mathes. She was educated in the local public schools and those of Portsmouth, New Hampshire before graduating from the Commercial College in Boston. She also had lessons with , with whom she collaborated on a number of works. She moved to Washington, D.C. sometime around 1900 and opened a studio at The Dewey. During her career she painted portraits of many notables, among them Edward Everett Hale, William Dean Howells, John D. Long and Frank Jones; she also painted portraits of at least ten mayors of Portsmouth. A portrait by Horne of Belva Ann Lockwood is currently owned by the National Portrait Gallery, while the portrait of Frank