I'm not entirely sure where you're getting that from, but this is from The Ohio State University:

To appreciate how violent the West was, we need to consider not only the annual homicide rate, but the risk of being murdered over time. For instance, the adult residents of Dodge City faced a homicide rate of at least 165 per 100,000 adults per year, meaning that 0.165 percent of the population was murdered each year—between a fifth and a tenth of a percent. That may sound small, but it is large to a criminologist or epidemiologist, because it means that an adult who lived in Dodge City from 1876 to 1885 faced at least a 1 in 61 chance of being murdered—1.65 percent of the population was murdered in those 10 years.

The crime in The Old West was significant, and they say earlier in the article that they know that they lowballed these numbers since these are only known numbers, not estimated. They do say as well that it's not as bad as the movies, but it was still astronomical by today's standards. It's a good read.