General John Alexander McClernand, born May 30, 1812, Kentucky, self- educated lawyer at age 20 and private in Blackhawk War with Abraham Lincoln as his Captain. Son of Dr. John, immigrant from Antrim, Ireland and Fatima Cummins (her ancestors were part of the Jamestown Colony). At age 24 he was a Democratic politician serving as a representative in Congress before the Civil War and as a subordinate commander to Ulysses Grant during the war. In November 1842, McClernand married Sarah Dunlap of Jacksonville, Illinois, a close friend of Mary Todd Lincoln. He resigned from the army due to health issues on November 30, 1864. Following the assassination of Lincoln the following year, McClernand played a visible role in the late president's funeral proceedings. In 1870, he was elected circuit judge of the Sangamon District of Illinois and remained in the post for three years before resuming his law practice. Still prominent in politics, McClernand presided over the 1876 Democratic National Convention. He later died on September 20, 1900, in Springfield, IL.
John and Sarah's son, Edward John McClernand, b1848, was notable as a U.S. Army Brigadier General in the Indian Wars and later in the Philippines, and awarded a Congressional Medal of Honor.
So, in researching this surname, I do not find a Sept, nor in any record have I or anyone else have been able to determine his ancestry past his parents. Taking Mc to mean son of and left with Clernand -the closest I can figure is perhaps Larnon from the Sept files. Anybody???
(For his brilliant military career, consult Wikipedia.)