In 1988, counties needed 64 percent more felony jail beds than they did in 1982. This increase in felony population was not because of longer jail times expected as part of sentencing reform, and it was not due to a shifting of sentences from State prison to county jail. Rather, the increase was the result of an increased number of sentenced felons, particularly those convicted of nonviolent offenses and a decrease in the use of community sanctions without accompanying jail time. Before the Sentencing Reform Act was implemented in 1984, county officials expressed fears that changes in felony sentencing patterns would adversely impact county jail populations. Using 1982 data, the Sentencing Guidelines Commission estimated that county jails would not experience population increases. To determine if this was the case, the commission collected 1988 data on felony sentences and jail times in the same 18 county jails included in the 1982 assessment. The impact of local policies on local jail populations was examined. Data on 1988 violations of sentence conditions revealed that it was not uncommon for jail time for the violation to exceed the jail time of the original sentence. Every fourth felon originally sentenced to jail was returned for alleged failure to comply with sentence conditions. On average, they stayed another 39 days in jail. The primary reason for an increase in jail population was the huge increase in the volume of felons. Between 1982 and 1988, the number of sentenced felons increased 54 percent. In addition, sentencing practices changed between 1982 and 1988. The percentage of felons sentenced to a community sanction only decreased from 24 percent of all felons to 7 percent. The number of days in county jail for felons sentenced to State prison increased slightly from 74 days in 1982 to 77 days in 1988. The number of days in county jail for felons sentenced to jail decreased from 64 days to 58.5 days. County summaries of jail felony populations are provided. 2 figures