Cosmo Nelson Innes FRSE (9 September 1798, Durris-on-Deeside – 31 July 1874, Killin) was a Scottish advocate, judge, historian and antiquary. He served as Advocate-Depute, Sheriff of Elginshire, and Principal Clerk of Session.
He was a skilled decipherer of ancient Scottish records and helped to compile, edit and index Acts of the Scottish Parliament 1124 - 1707. He was said to be tall, handsome but very shy. He was accused of being a Catholic sympathiser (whilst it remained illegal) and joined the newly created Scottish Episcopal Church (very close in its practices to Catholicism). Dean Ramsay, head of the Episcopal Church, was one of his good friends.
Born in Durris Castle to John Innes of Leuchars WS and Euphemia Russell. His middle name, Nelson, is almost certainly to mark Horatio Nelson's then very recent victory at the Battle of the Nile in August 1798. Thirteen of his fourteen siblings died, only he and his sister Elizabeth survived. His friends included Alexander Forbes Irvine (1818-1892), whose career closely paralleled his own.
He was educated at Edinburgh High School, then at Edinburgh University under Prof James Pillans. He then did further studies at Aberdeen, Glasgow Universities, and at Balliol College, Oxford (1817-1820) graduating BA in 1820. He was admitted to the Faculty of Advocates in 1822, and was appointed Professor of Constitutional Law and History in the University of Edinburgh in 1846.