840 AM may refer to:

In Canada

• CKBX in 100 Mile House, British Columbia

In Mexico

• in Campeche, CM
• in Celaya, GT
• in Celaya, GT
• in Izucar de Matamoros, PU
• in Tuxtla Gutierrez, CS
• in Tuxtla Gutierrez, CS
• XEMY in Cd.Mante, TA
• in Cd.Mante, TA
• in Navojoa, SO
• in Papantla, VC
• in Tepic, NA
• in Chilpancingo, GR

In the United States

• in Eugene, Oregon
• in Colfax, Washington
• in Modesto, California
• KSWB (AM) in Seaside, Oregon
• in West Point, Nebraska
• in Pharr, Texas
• in Ball, Louisiana
• in North Las Vegas, Nevada
• in Mobile, Alabama
• WCEO in Columbia, South Carolina
• in Louisville, Kentucky
• in Denton, Maryland
• in Earlysville, Virginia
• in Mims, Florida
• in New Britain, Connecticut
• in Stroudsburg, Pennsylvania
• in Yabucoa, Puerto Rico