Approximately 20 fire companies from Massachusetts and northern Rhode Island responded to a four-alarm fire Monday night at a large home in Uxbridge, a firefighter said. Lieutenant Keith Carter of the Pascoag, R.I., fire department said crews responded shortly after 11 p.m. Monday to a fire in a “big, old farmhouse” on Hartford Avenue in Uxbridge, about 30 miles southwest of Boston. Carter was part of a mutual-aid company on standby at the Uxbridge fire department and had not been at the scene of the fire. He was unable to say if anyone was home when the fire began or if there were any injuries.