The highest imprisonment rates for the period were for crimes of larceny. The percentage of murderers in the prison increased in 1855, 1864, 1859, and 1857. Census estimates for the period indicate that Irish immigrants composed approximately 18 percent of the population in Schuylkill County from 1860 to 1870. Irish immigrants composed approximately 45 percent of the prison population in the county from 1853 to 1870. They were more likely to be incarcerated than any other ethnic group in the county. Inmates' most common occupations during the period were as laborers and miners. The analysis of prison data suggests that an ethnic bias may have been prevalent not only within the Schuylkill County criminal justice system from 1853 to 1870 but also within the county's communities. The northeastern Pennsylvania coal mining industry expanded greatly between 1860 and 1870, and one-third of all mineworkers were Irish. As an occupational group, the Irish outnumbered immigrant and second-generation Welsh and English miners combined; however, mining management personnel were Welsh or English, as were the men who held the skilled "craft miner" positions. The Irish were left with the jobs of lower salaried laborers who extracted the coal. This set the stage for labor and ethnic conflict, with much of the violence between 1862 and 1876 attributed to the secret Irish society called the Molly Maguires. This article drew on descriptive and statistical data from Annual Reports of the Schuylkill County Prison, 1853-1870, and census records (1870-1900) collected and analyzed by Molly Maguire historian Howard T. Crown. 3 figures and 12 references