Wyatt Earp was born in Monmouth, Illinois, on March 19, 1848, to widower Nicholas Porter Earp and Virginia Ann Cooksey. From his father's first marriage, Wyatt had an elder half-brother, Newton, and a half-sister Mariah Ann, who died at the age of ten months. Wyatt was named after his father's commanding officer in the Mexican-American War, Captain Wyatt Berry Stapp, of the 2nd Company Illinois Mounted Volunteers. In March 1849, the Earps left Monmouth for California but settled in Iowa. Their new farm consisted of 160 acres (0.65 km2), 7 miles (11 km) northeast of Pella, Iowa.
On March 4, 1856, Earp's father Nicholas sold his farm and returned to Turtle, Illinois, where he was elected the municipal constable, serving at this post for about three years. He was caught and convicted in 1859 for bootlegging. Nicholas was unable to pay the fines, and a lien was put against the Earp's property. It was sold at auction in November 1859, and the family left again for Pella, Iowa. After their move, Nicholas returned to Monmouth throughout 1860 to sell his other properties and resolve several lawsuits for debt and accusations of tax evasion.
During the family's second stay in Pella, the American Civil War began. Newton, James, and Virgil joined the Union Army on November 11, 1861. While his father was busy recruiting and drilling local companies, Wyatt, along with his two younger brothers, Morgan and Warren, were left in charge of tending 80-acre (32 ha) corn crop. Only 13 years old, Wyatt was too young to enlist, but he tried on several occasions to run away and join the army. Each time his father found him and brought him home. James was severely wounded in Fredericktown, Missouri, and returned home in the summer of 1863. Newton and Virgil fought several battles in the east and later returned. On May 12, 1864, the Earp family joined a wagon train heading to California.
By late summer 1865, Virgil found work as a driver for Phineas Banning's Stage Coach Line in California's Imperial Valley, and 16 year old Wyatt assisted. In the spring of 1866, Wyatt Earp became a teamster, transporting cargo for Chris Taylor. His assigned trail for 1866–1868 was from Wilmington, through San Bernardino and Las Vegas, Nevada, to Salt Lake City, Utah Territory.
In the spring of 1868, Earp was hired by Charles Chrisman to transport supplies for the construction of the Union Pacific Railroad. He learned gambling and boxing while working on the railhead in Wyoming, and refereed a fight between John Shanssey and Mike Donovan.
In the spring of 1868, the Earps moved east again to Lamar, Missouri, where Wyatt's father Nicholas became the local constable. Wyatt rejoined the family the next year. When Nicholas resigned on November 17, 1869 as constable to become the justice of the peace, Wyatt was appointed constable in his place. On November 26, in return for his appointment, Earp filed a bond of $1,000. His sureties for this bond were his father, Nicholas Porter Earp; his paternal uncle, Jonathan Douglas Earp (April 28, 1824–October 20, 1900); and James Maupin.
 Jane Eppinga (2010). Tombstone. Arcadia Publishing. p. 41.
 Where was Nicholas Earp in 1849-50?
 Urban, William. "Nicholas Earp".
 Woog, Adam (February 28, 2010). Wyatt Earp. Chelsea House Publications. p. 110. ISBN 1604135972.
 Wyatt Earp: Timeline - Child hood to Wichita.
 WGBH American Experience: Wyatt Earp, Complete Program Transcript. January 25, 2010.