Patrick Flynn was born on May 11, 1833, in County Mayo, Ireland. He immigrated to America around 1847 and settled in Rockford, Illinois, around 1858. By 1860, he was working as a saloon keeper there, and he owned $700 of personal property. When the Civil War erupted, one writer later noted, he “espoused the cause of his adopted country with a lover’s devotion.”
On August 1, 1862, he received a commission as a captain in Company A of the 90th Illinois Infantry. According to his service records, he was 5 feet, 7 inches tall, with auburn hair and hazel eyes. The regiment took part in the siege of Vicksburg, the Battle of Missionary Ridge, and the Atlanta campaign. He was promoted to major on March 6, 1863. He was wounded in Atlanta, Georgia, and he lost the use of his right arm. He mustered out on May 15, 1865.
Flynn returned to Rockford after the war. He married a woman named Mary, and they had at least two children: Mary, born around 1869; and Katherine, born around 1873. He joined the Republican Party, and by 1870, he was working as a sheriff and jailer. That year, the family owned $4,250 of real estate and $1,000 of personal property. A decade later, he was working as a detective. His wife died on November 28, 1892. By 1900, Flynn was working as a government official in the Internal Revenue Service. He died on October 17, 1901.