Maximillian "Max" Parker was born 8 June 1844 in Accrington, Lancashire, England. He was the oldest of nine children of Robert Parker and Ann Ruth Hartley. The family lived in Old Accrington until they joined the Mormon Church in 1852 and moved to Preston, Lancashire, England. There, Max was assigned to polish the shoes of the missionaries who boarded with his family. He was apprenticed at the local woolen mill (his father was a weaver) but didn't like it, so one day he ran away. This disgraced the family, and crystalized their plans to immigrate to America in May 1856.

The family sailed on the "Enoch Train" from Liverpool to Boston, arriving 1 May 1856. They continued by boat and rail to Iowa City and then crossed the plains to the Great Salt Lake Valley by handcart, arriving 26 September 1856. (Note: this family was the one in the revered pioneer story of the mother giving the father a shawl as he left to find their lost son, and told him to wrap or bury him in it).

The family lived in American Fork, Utah County, and then Beaver, Beaver County, where they lived and farmed. As a young man, Max guided many trains of settlers from the Missouri River to Utah Territory. He was one of the leaders in the construction of old Fort Sanford, near Panguitch, in 1864.

He was a private in Captain Edward Dalton's company of the Utah Territorial Militia (Cavalry) during the Blackhawk War. He enlisted 21 March 1866 in Parowan, Utah, and was discharged 21 June 1866. He later filed for a pension in 1907.

Max married Annie Campbell Gillies in 1865 in Salt Lake City, Salt Lake, Utah Territory. They had thirteen children, including their oldest son Robert Leroy Parker, better known as Butch Cassidy. Max carried the mail between Beaver and Panguitch along the Sevier River. In 1879, Max moved his family to Circle Valley, which he had passed on his mail route. He built a log cabin and planted summer wheat. He then looked for employment, and one of his first jobs was cutting and hauling wood at the Silver Reef Mine, nearly a 100-mile drive from home.

When the work slowed down, he started freighting timber for the charcoal smelters at Frisco, Utah, and Pioche, Nevada.

On the 1880 census, Max was a farmer, living with his wife and seven children in Circleville.

Over the next two decades, the family lived in Spry and Antimony in Garfield County, in Beaver, and Circleville in Piute County.

Robert Leroy Parker was born April 13, 1866, in Beaver, Utah, the first of 13 children born to British immigrants Maximillian Parker and Ann Campbell Gillies. The Parker and Gillies families had converted in England and Scotland to the Mormon faith and immigrated to Utah. Maximilian Parker was 12 when his family arrived in Salt Lake in 1856 as Mormon pioneers; Ann Gillies arrived with her family in 1859, aged 14. The two were married in July 1865.

In 2008 documented evidence highlighted, Ann Gillies, the mother of Butch Cassidy, was born and lived on Tyneside, in the north east of England, before moving to America with her parents, where she later married Butch's father, Maximilian Parker, in Utah.

Robert grew up on their ranch near Circleville, Utah, 346 km (215 mi) south of Salt Lake City. He left home during his early teens. While working at a dairy farm, he formed a close relationship with his mentor, a cowboy and cattle rustler who called himself Mike Cassidy (an alias for John Tolliver "J. T." McClammy). Parker subsequently worked at several ranches, in addition to a brief stint as a butcher in Rock Springs, Wyoming, when he acquired the nickname "Butch", to which he soon appended the surname Cassidy in honor of his old friend.