The objective of this study was to characterize population-based emergency medical service (EMS) use rates and examine some of the factors associated with usage of prehospital services. The design was a population-based observational study with multiple regression analysis. Transports reported by prehospital services to the Kentucky Emergency Medical Services Information System from Kentucky counties in which all EMS units submit computerized data was the data source. There were 102,321 emergent transports reported. The overall rate of use of EMS transports was 51.7 +/- 24.1/1,000/year, but the rate varied between different communities (range 11 to 139/1,000/year). Rate of use was highest in those older than 65 (178.5 +/- 84.2/1,000/year), with the rate increasing exponentially with increasing age in this age group. Reasons for transport were age dependent. There was an association between increasing poverty level and use of EMS. In addition, the absence of 911 service (odds ratio [OR] 1.18, 95% confidence interval [CI; 1.14,1.22]) and the absence of a hospital in the county (OR 1.27, 95% CI [1.24,1.30]) were also associated with increasing rates of ambulance use. Rates of use of EMS are most dependent on age and cause, but use is also correlated with increasing levels of poverty. Wide variations in use between communities suggests that point estimates using one community may over- or underestimate EMS usage.