The magistrates' court in Cirencester has begun hearing crown court cases one week a month to help ease pressure at Gloucester.
HM Courts Service is equipping the building to deal with crown court hearings, including making provision for juror facilities.
The number of offences put before the courts in the county has greatly increased since 2004.
Overspill cases at Gloucester had, until now, been transferred to Bristol.
Magistrates', county and coroner's court sessions will continue to be held at Cirencester as usual.
Rod Brummitt, area director for Her Majesty's Courts Service, said: "The decision to move cases to Cirencester has been taken to ensure that cases are heard promptly, enabling us to continue delivering first class justice to the Gloucestershire public.
"It will also enable us to reduce the inconvenience to court users caused previously when some cases had to be transferred to Bristol because there was insufficient space at Gloucester.
"This is an interim measure as we hope to be able to build a new criminal court for both crown and magistrates' business in the not-too-distant future."