Schuyler County is a county located in the northeastern portion of the U.S. state of Missouri. As of the 2020 census, its population was 4,032, making it the fourth-least populous county in Missouri. Its county seat is Lancaster. The county was organized February 14, 1845, from Adair County, and named for General Philip Schuyler, delegate to the Continental Congress and U.S. Senator from New York.

Adair County is a county located in the northeastern part of the U.S. state of Missouri. The population census for 2020 was 25,314. As of July 1, 2021, the U.S. Census Bureau's Population Estimates for the county is 25,185, a -0.5% change. Adair county seat is Kirksville. The county was first settled by immigrants from Kentucky and organized on January 29, 1841. Adair County comprises the Kirksville, MO Micropolitan Statistical Area.