Mercer County - Missouri [Back to Main] County Information Population: 3,757 Average Income: $29,640 Area: 454 sq. miles Cities: Mercer, Princeton, South Lineville Service Providers Company Name and Location(s) Serviced Services Provided and Costs Grand River Mutual [Link] Mercer, Princeton, South Lineville DSL Modem and installation fees depend on contract agreement. 1.5mbit - $42.95/month Green Hills Telephone Co. [Link] Mercer, South Lineville wireless Free modem and installation with 1 year contract. 1mbit - $39.95/month