Marana Unified School District announced it would require everyone on its campuses to wear masks indoors starting Monday.
Schools around Pima County reported 914 COVID-19 cases between July 20 and Aug. 20.
State health officials reported 2,632 new cases across Arizona on Monday.
The state Legislature banned school districts from requiring students to wear masks and Gov. Doug Ducey has sought to discourage districts from adopting such requirements. He announced last week that millions of dollars in federal grant money for school districts would only be provided to districts that are "following all state laws."
But Marana Unified School District said the policy will help reduce the number of COVID-19 cases in the school and will only extend through September 28, the day before the new state law takes effect.
The district is also providing exemptions from the policy for staff and students based on either documented medical needs or religious beliefs.