Jonas Hartzell McGowan (April 2, 1837 – July 5, 1909) was a politician from the U.S. state of Michigan.
McGowan was born in Smith Township, Ohio (then part of Columbiana County, now Mahoning County). He was the eighth of ten children of Samuel and Susan McGowan. His paternal Scotch-Irish ancestors had fled religious persecution and settled in Pennsylvania. His father was a pioneer in Columbiana County, Ohio, where he cleared a tract of government land and occupied it as a homestead. In 1854, Samuel moved his family to Orland, Indiana, where he died in 1860. McGowan's mother was of German descent and survived the father for another four years. McGowan's father was an abolitionist and his house served as a depot on the Underground Railroad.
McGowan attended a seminary in Alliance, Ohio and the Orland Academy. He graduated from the University of Michigan at Ann Arbor in 1861 and taught in the city schools of Coldwater, Michigan for one year. In 1862, he married Josephine Pruden, then preceptress at the High School in Coldwater.
During the Civil War, McGowan served in the Fifth and Ninth Regiments, Michigan Volunteer Cavalry. In August 1862, he enlisted as a private in the Fifth Regiment and was soon promoted to Sergeant of his Company. In November 1862, he was made a Captain in the Ninth Regiment, and went into the field early in 1863. Their first service was chasing Confederate General John Hunt Morgan, who made incursions into southern Indiana and Ohio on Morgan's Raid. McGowan took part in the Battle of Salineville, which resulted in the capture of Morgan in July 1863, near Salineville, Ohio. He went into campaigns in East Tennessee with General Ambrose Burnside, until he was forced to resign in 1864 for reasons of poor health.