Isaac Phillips Caldwell was born in Pennsylvania on September 21, 1835, to James and Isabella Caldwell. He received his early education in Fayette County, Pennsylvania. By 1850, the family had moved to Preston County, Virginia (now West Virginia), where James worked as a merchant and tavern keeper.  

In 1851, Caldwell enrolled at Dunlap's Creek Academy in Fayette County, Pennsylvania. Then from 1854 to 1856, he attended the University of Virginia, where he studied ancient languages, mathematics, and moral philosophy. He settled in Richmond, Missouri, after leaving UVA, becoming a lawyer and a probate court judge. 

Caldwell remained loyal to the Union during the Civil War and swore an oath of allegiance to the United States government. Between August 7 and August 21, 1862, he served as a private in the 25th Missouri Enrolled Militia, a part-time military force that helped protect the state’s garrisons and infrastructure from Confederate guerrillas. His family struggled to make ends meet during the war, and in 1863 Caldwell reported living in a “destitute condition.” That October, he asked a local officer for permission to travel to Adams County, Illinois, to “try to get a load of Potatoes Cabbage ++.” 

Caldwell later served as a teamster under Captain William Craig, quartermaster at Fort Union in New Mexico. He worked as both a “civilian packer” and wagon master at the fort for several months until his discharge on October 5, 1864. Caldwell then returned to Missouri, where he proudly declared himself one of the state’s “Loyal Citizens.” In early 1865, he petitioned Union officers to arrest a local woman for declaring that she had “hurrahed for Jeff Davis and would do it whenever she pleased.”   

On April 24, 1865, he married Sarah Margaret Frame, the daughter of a Missouri lawyer. They had at least three children: Miriam, born 1867; Jane, born 1870; and James, born 1876. In 1872, Caldwell was the Republican candidate for judge of the 28th Judicial Circuit in Missouri, but he lost to the nonpartisan candidate Samuel Richardson. By 1876, the family had settled in Laramie in the Wyoming Territory.

In 1887, Caldwell helped prepare the Revised Statutes of Wyoming, and two years later he helped frame the new state's constitution. He served in the Wyoming General Assembly and served several terms as mayor of Laramie. After the Panic of 1893, he moved to Denver, Colorado, where he remained for the rest of his life. He filed a pension application in 1906, but the War Department declined it because he had never been mustered into federal service. Caldwell died in Denver in November 1916. Shortly after, a Colorado writer remembered him as a “staunch republican” who “labor[ed] untiringly to advance the interests of his party in state and national elections.” He was a “man who commanded and enjoyed the respect, confidence, and honor of those who knew him.”

Document:

Service Record for Isaac P. Caldwell

Isaac P. Caldwell Asks Permission to Travel to Illinois

Isaac P. Caldwell Runs for Circuit Court Judge