Sir Jenkin Coles KCMG (19 January 1843 – 6 December 1911) was an Australian politician, a speaker in South Australia.
Coles was the son of Jenkin and Caroline Coles, came of an old north of Ireland family, and was born at Liverpool, New South Wales. When he was seven years old his family returned to Europe, and he was educated at Christ's Hospital School, London.
Coles' parents came to Australia again in 1858 and settled at Adelaide, South Australia. Coles obtained a position as a junior clerk with the Murray River Navigation office, but gave this up to become assistant dispenser and receiver of stores at the Adelaide hospital for three years. He then joined the mounted police and served for three years in the country. On leaving this service he became an auctioneer and stock salesman and a member of the firm of Coles and Goodchild. The business prospered so much that Coles was able to practically retire from it before he was 40. He was returned to the South Australian House of Assembly as member for Light in 1875, but did not stand at the 1878 election as he found that the strain of carrying on both business and parliamentary duties was too great. In 1881 he was elected for Light, afterwards merged in Wooroora, and represented the district for over 30 years. He was commissioner of crown lands from June 1884 to February 1885, and commissioner of public works from February to June 1885 in the second John Colton ministry and showed himself to be a vigorous administrator. He was commissioner of crown lands again in the Thomas Playford II ministry from June 1887 to June 1889. In 1890 he was elected speaker of the house of assembly in succession to Sir John Bray, and held the position until he resigned, about three weeks before his death of Bright's disease on 6 December 1911. He married in 1865 Ellen Henrietta Briggs, who survived him with four sons and seven daughters. He was created K.C.M.G. in 1894.
Coles was speaker for over 21 years, a record in Australia, and until his last illness never missed a sitting. He had a great knowledge of the standing orders and was firm, tactful, alert and wise. He was thoroughly respected on both sides of the house, his rulings and requests were always obeyed, and under his sway the house of assembly in South Australia established a high reputation for the orderly conduct of its business.