Sir William Edmond Logan (April 20, 1798 - June 22, 1875) was a noted 19th century Canadian geologist.

Logan was born in Montreal, Quebec and studied at the university of Edinburgh. He started teaching himself geology in 1831, when he took over the running of a colliery in Swansea. He produced a geological map of the south Wales coalfield, and gave his opinion that the layer of clay under the coalfield was the old soil in which grew the plants from which the coal was formed.

His abilities as a geologist were noticed, and in 1842 he was asked to establish the Geological Survey of Canada. He continued as director until 1869. During this time he described the Laurentian rocks of the Laurentian mountains in Canada and of the Adirondacks in the state of New York.

Over his illustrious career he received 22 medals including the Legion of Honor from Emperor Napoleon III of France in 1855 and a knighthood from Queen Victoria of England in 1856. In the same year he was awarded the Wollaston Medal by the Geological Society of London.

After his retirement in 1869 he settled in Pembrokeshire, where he died. He was interred in the churchyard in the village of Cilgerran.

The highest mountain in Canada, Mount Logan, was named after him. As well, the mineral Weloganite, first found in Montreal, is named after him.