There are 19 US Post Offices in Macoupin County serving a total of 44,813 residents equating to 2,359 residents per post office. It's estimated that approximately 71,527 packages are handled across the 19 county post offices annually. Macoupin County is a county located in the southwestern portion of the U.S. state of Illinois. According to the 2010 census, it had a population of 47,765. The county seat is Carlinville. Macoupin County is part of the Metro-East region of the St. Louis, MO-IL Metropolitan Statistical Area. The primary industry is agriculture, consisting of crops of corn (maize), soybeans, and some wheat."