As Warren County taxpayers prepare to take on a debt of $9 million for an “unavoidable” expansion of the jail, they need look no further than the local drug culture as the main force behind the exploding population of inmates.That is the assessment of retiring Sheriff Jackie Matheny in a farewell address at The Rotary Club of McMinnville and during a WCPI interview recorded Thursday.Asked in the radio interview to estimate what portion of the daily jail census, recently averaging 318 inmates, should be attributed to illegal drug use, the veteran lawman replied, “75 to 80 percent, possibly higher.”Matheny formally retired Friday after serving 24 consecutive years as Warren County sheriff. Prior to his first election to that office, he worked eight years as a patrol officer with McMinnville Police Department. It was during that duty he was shot and seriously wounded by a drunken driver who tried to flee pursuing officers.But the good experiences outweigh the bad, he said, as he derived pleasure and satisfaction from helping people, especially in their times of crisis and hardship.