The policy includes tobacco use by patrons at sports events.
The previous policy banned tobacco use in district buildings.
Alton School District Superintendent Sheila Wheeler said a board member brought the issue to the school board because many spectators gather to smoke outside buildings during basketball, volleyball and other games.
"We felt it was time to do something," Wheeler said. "There would be people smoking right outside the doors. We'd find cigarette butts on the ground."
Wheeler said the new policy will promote a cleaner, safer environment for students, and discourage tobacco use.
Couch Schools adopted a tobacco-free district policy in October 2002, while Thayer School District adopted a similar policy in April 2009.
Thayer School District Superintendent Dan Chappell said Thayer "probably doesn't enforce" the policy as good as it should during ball games.
Still, the policy makes a difference in keeping school grounds cleaner and reducing smoking, he said.
Comparing cigarette use today to 20 or 30 years ago, Chappell said such policies against smoking in public places have made a difference in reducing tobacco use.
"I think it definitely helps," Chappell said. "It is a lot better now than it was when I was growing up."
The policies state: "The district prohibits all employees, students and patrons from smoking or using tobacco products in all district facilities, on district transportation and on all district grounds at all times. This prohibition extends to all facilities the district owns, contracts for or leases to provide educational services, routine health care, day care or early childhood development to children."