The use of hypofractionated radiotherapy (HFRT) in patients with breast cancer and ductal carcinoma in situ (DCIS) in Ontario, Canada, from 2009 to 2015 was reported. A retrospective cohort study was conducted using data from the Institute for Clinical Evaluative Sciences (ICES). Patients with a breast cancer or DCIS diagnosis between 2009 and 2015 who received adjuvant breast or chest wall radiation were included. Trends in HFRT use (≤16 fractions) and factors associated with HFRT use in a multivariable logistic regression model with physician-level random effect were reported. The approximate number of hours that could be saved if all patients were to receive HFRT was calculated. A total of 42 072 patients were included. All included characteristics were significantly associated with HFRT use. Hypofractionated radiotherapy use in patients with breast cancer and DCIS increased to around 75% in 2015. In stage I/II patients with mastectomy and chest wall radiation, HFRT use increased to 40% in 2015. Hypofractionated radiotherapy use in patients with regional nodal radiation or reconstruction has increased but remains under 20%. For breast cancer patients with breast-conserving surgery (BCS) and breast radiation, 56 265 visits corresponding to 7200 hours of treatment or 3500 additional HFRT courses could have been saved. In conclusion, HFRT use in Ontario has increased in all patient populations but is nonuniform among physicians and institutions. Use of HFRT in chest wall and regional nodal radiation remains relatively lower than in breast cancer and DCIS patients with BCS.