Background: We aimed to better understand the impact of statewide legislation removing personal belief exemptions (PBEs) for the measles, mumps, and rubella (MMR) school immunization requirement and factors associated with resulting health-seeking behaviors. Methods: We used chi-squared tests and logistic regression models to determine individual- and school-level characteristics associated with holding a MMR PBE and with post-law MMR immunization status among students linked to the Washington State Immunization Information System. Results: Of students with a MMR PBE pre-law change, 43.0% completed the MMR vaccine series and 40.4% sought another exemption type. Religious exemptions made up most new MMR exemptions signed (71.8%), followed by medical exemptions (18.5%), and religious membership exemptions (9.7%). Students were more likely to complete the vaccine series post-law change if they attended a school with a low school-level MMR exemption rate, a public school, or held a lower number of school-required immunization exemptions. Conclusions: This study confirms previous concerns that parents might replace their PBE with another exemption type; however, nearly half the students in the cohort completed the MMR vaccine series. Our findings suggest that targeted immunization policies can increase MMR coverage 1-year post-law change but must account for a replacement effect when exemption categories are eliminated.