A report by the state's Office of Policy and Management put the Jan. 1 count at 17,746 inmates, down from 18,053 in December.
That's the fewest number of inmates in the system since 2001.
The report says the decrease in the prison population is due to a decline in the number of people entering the system after arrests or convictions and a slight increase in the number of people released from prison.
The report notes that 21 percent of the total prison population are inmates awaiting trial. That's up from 17 percent in 2001.