Officials from eight counties selected according to jail size were interviewed. Parameters from site visits were used to estimate jail costs. The jails selected ranged in capacity from 5 to 41 prisoners. In addition, costs from the sample of local jails were compared to costs from studies of larger jails and state prisons. Jails with 5 to 41 bed capacity exhibited a U-shaped cost curve. Jail costs varied from a low of $35.20 per prisoner day for the 10 bed jail to $56.63 per prisoner day for the 40 bed jail. Therefore, costs vary by $21.43 per prisoner day for the sample of local jails examined in this study. The threshold economies of size achieved by smaller jails is due primarily to the shared staffing systems, a high degree of integration between jail functions and law enforcement / communications dispatcher functions, and variation in square footage of space per inmate.