John Barham Day (1793–1860) was a British jockey and trainer. For much of his career he was usually known simply as John Day; when his son of the same name rose to prominence, the older man was referred to as John Barham Day, John Day, Sr. or Old John Day. A member of a highly successful racing family, Day first made his name as a jockey in the 1820s and rode the winners of sixteen classics before retiring. In the mid-1830s he set up as a trainer of racehorses at Danebury near Stockbridge. He established a reputation as a shrewd and skillful handler of horses and specialised in landing betting coups. Horses trained by Day won seven classics between 1838 and 1854, during which time he was regarded as the leading trainer in the South of England and the main rival of the Yorkshire-based John Scott. He was known as "Honest John", but the sobriquet appears to have been applied ironically.

John Day was a British jockey and trainer. A member of a large and highly successful racing family Day was sometimes known as Young John Day or John Day, Jr. to distinguish him from his father John Barham Day. The younger John Day had some success as a jockey before taking over from his father as the trainer at the Danebury stables in 1847. In a training career of over thirty years Day sent out the winners of twelve classics including three winners of The Derby. Like many trainers of his time, Day was a heavy gambler and clashed on several occasions with other leading turf figures.