21 killed - July 18, 1984 - In San Ysidro, California, 41-year-old James Huberty, armed with a long-barreled Uzi, a pump-action shotgun and a handgun shoots and kills 21 adults and children at a local McDonalds. A police sharpshooter kills Huberty one hour after the rampage begins.
18 killed - August 1, 1966 - University of Texas. Charles Joseph Whitman, a former U.S. Marine, kills 16 and wounds at least 30 from a university tower. Police officers Ramiro Martinez and Houston McCoy shot and killed Whitman in the tower. Whitman had also killed his mother and wife earlier in the day.
13 killed - September 25, 1982 - In Wilkes-Barre, Pennsylvania, 40-year-old George Banks, a prison guard, kills 13 people including five of his own children. In September 2011, the Pennsylvania Supreme Court overturns his death sentence stating that Banks is mentally incompetent
9 killed - January 7, 1973 - In New Orleans, Louisiana, 23-year-old Mark Robert James Essex, using a .44 magnum carbine, kills nine people in a rampage at a Howard Johnson motel. Police snipers later kill him.
8 killed - September 14, 1989 - In Louisville, Kentucky, 47-year-old Joseph Wesbecker armed with a AK-47 semiautomatic assault rifle, two MAC-11 semiautomatic pistols, a .38 caliber handgun, a 9-millimeter semiautomatic pistol and a bayonet kills eight co-workers at Standard Gravure Corporation and then kills himself. He had been placed on disability leave from his job due to mental problems
8 killed - May 17, 1984 - In Manley Hot Springs, Alaska, 25-year-old drifter Army veteran Michael Silka kills eight people in a three-hour rampage. Two days later, Silka is killed in a shootout with police.
Here you go...