Question: When was the prison relocated to  Warren in Knox County, Maine, United States?
Context: Rockland is a city in Knox County, Maine, in the United States.  As of the 2010 census, the city population was 7,297.  It is the county seat of Knox County.  The city is a popular tourist destination.  It is a departure point for the Maine State Ferry Service to the islands of Penobscot Bay: Vinalhaven, North Haven and Matinicus. Downeast Airlines Flight 46 was a scheduled airline service in the United States from Boston's Logan International Airport to Rockland, Maine operated by Downeast Airlines.  On May 30, 1979 a de Havilland Canada DHC-6 Twin Otter operating the flight crashed during a nonprecision approach to Rockland's Knox County Regional Airport.  The cause of the accident was controlled flight into terrain (CFIT) after the failure of the flightcrew to stop the aircraft's descent below the minimum descent altitude for the nonprecision approach at Knox County airport.  The investigation into the accident looked into the airline's corporate culture as a contributing factor to the crash; this was the first time an investigation took this approach to an air crash. Warren is a town in Knox County, Maine, United States.  The population was 4,751 at the 2010 census.  It includes the villages of East Warren, Warren and South Warren, the latter home to the Maine State Prison and minimum security Bolduc Correctional Facility. Knox County Regional Airport (IATA: RKD, ICAO: KRKD, FAA LID: RKD) is a county owned, public use airport in Knox County, Maine, United States.  It is located three nautical miles (6 km) south of the central business district of Rockland, Maine.  The airport serves the residents of midcoast Maine with commercial and charter aviation services.  Scheduled airline service is subsidized by the Essential Air Service program.  It is also a major hub of freight and mail service to Maine's island communities including Matinicus, North Haven and Vinalhaven. Knox County Airport (FAA LID: 4I3) is a public use airport located four nautical miles (7 km) southwest of the central business district of Mount Vernon, a city in Knox County, Ohio, United States.  It is owned by Knox County Airport Authority. North Haven is a town in Knox County, Maine, United States, in Penobscot Bay.  The town is both a year-round island community and a prominent summer colony.  The population was 355 at the 2010 census.  North Haven is accessed by three-times daily ferry service from Rockland, or by air taxi from Knox County Regional Airport. Vinalhaven is a town located on the larger of the two Fox Islands in Knox County, Maine, United States.  Vinalhaven is also used to refer to the Island itself.  The population was 1,165 at the 2010 census.  It is home to a thriving lobster fishery and hosts a summer colony.  Since there is no bridge to the island, Vinalhaven is accessible from Rockland via an approximately hour-and-fifteen-minute ferry ride across West Penobscot Bay, or by air taxi from Knox County Regional Airport. Owls Head is a town in Knox County, Maine, United States.  The population was 1,580 at the 2010 census.  A resort and fishing area, the community is home to the Knox County Regional Airport.  It includes the village of Ash Point. Knox County is a county located in the state of Maine, in the United States.  As of the 2010 census, the population was 39,736.  Its county seat is Rockland.  The county is named for American Revolutionary War general and Secretary of War Henry Knox, who lived in the county from 1795 until his death in 1806.  The county was established on April 1, 1860, and is the most recent county to be created in Maine.  It was carved from parts of Waldo and Lincoln counties.  The Union Fair, started in 1868, began as the efforts of the North Knox Agricultural and Horticultural Society. The Maine State Prison was erected in Thomaston, Maine in 1824 and relocated to Warren in 2002.  This maximum-security prison has a capacity of 916 adult male inmates with an average daily population of 900.
Answer: 2002