Both Rutherford and Williamson counties in Tennessee issued mask mandates this summer. Williamson county started theirs on July 8th, while Rutherford county waited until July 22nd. On July 8th, both counties were experiencing a weekly average of 25 new cases each day per 100,000 people. Eleven days later, Williamson County peaked at 45 new cases per 100,000 on July 19th and then started dropping dramatically. Rutherford county waited until July 22nd to issue a mask mandate. New cases in Rutherford county began a significant drop five days later. New cases in both counties reached a similar low level at the end of August – between 12.5 and 14.5 new cases per 100,000 people.
That is where the good news ends. Williamson county allowed their mask mandate to expire on August 31st. New cases for Williamson county bottomed out five days later a little below 10 new cases per 100,000 people, and have since increased 46%. See the graph below.
Both counties showed that mask mandates work at reducing the spread of COVID-19. Williamson county also demonstrated that lifting a mask mandate will lead to an increase in cases.
Both counties have experienced an increase in new cases since the beginning of September, possibly due to the impact of re-opening schools, colleges, and universities. However, Rutherford county has experienced a much smaller increase. Since the first of the month new cases in Rutherford county have increased 18%, which is less than half the increase experienced in adjacent Williamson county. Rutherford county ended its mask mandate on September 22nd, which will almost certainly lead to a significant increase in new cases in the weeks ahead.