The objective of this study was to evaluate the association of asthma hospital visits with ozone concentrations in Maricopa County, Arizona. We used time plots and distributed lag nonlinear models to achieve these objectives while accounting for some potential confounders including temperature and day of the week. A total of 90,381 asthma hospitalizations were retrieved from the dataset (daily median = 39, range: 8–122). Asthma hospitalizations were highest in 2008 (16,949), during the months of November through December, and lowest in 2011 (13,213), during the months of June through July. By contrast, the average daily ozone concentration ranged from 27.05 parts per billion (ppb) in 2012 to 30.15 ppb in 2008 and from 13.96 ppb in December to 40.58 ppb in May. The association between asthma hospitalizations (relative risk [RR/per 10 ppb increase of ozone]) start at ~1.046 (95% confidence interval [1.029, 1.064] at lag 0) and gradually decrease over several days. Our findings suggest exposure to ozone is associated with increased RR of asthma hospital visits in Maricopa County lasting several days. This study used recently developed methods that are freely available and could be used to evaluate other health events that are measured over time.