After the war Allison moved to Texas and took herds to Colorado, Kansas and New Mexico. A heavy-drinking cowboy he was accused of killing Chunk Colbert in Colorado and Francisco Griego in New Mexico. He also wounded several others before killing Deputy Sheriff Charles Faber at Las Animas in 1877. One newspaper claimed that Allison had killed 15 men.
Allison settled in Pecos, Texas and one neighbour claimed that "when sober he was a quiet, pleasant, affable man, but under the influence of liquor he was a very dangerous man."
On 3rd July, 1887 Clay Allison fell off the freight wagon he was driving and one of the wheels ran over his head. He fractured his skull and later died from his injuries.