in november 1842, mcclernand married sarah dunlap of jacksonville, illinois, a close friend of mary todd lincoln. sarah was a daughter of james dunlap, who served as a quartermaster in the union army during the civil war, eventually appointed to the rank of brevet major general. john and sarah's son, edward john mcclernand, was notable as a u.s. army brigadier general in the indian wars and later in the philippines. after sarah's death, mcclernand married her sister, minerva dunlap.