If you mean a marriage license, that can be obtained at the Montgomery County Courts building on Perry Street in Dayton. It's located on the second floor.
Unmarried license? Here you obtain birth and death records. At the health center you can get immunizations, prophylactics and other services.
You can order Montgomery County vital records here: https://www.vitalchek.com/vital-records/ohio/montgomery-county-vital-records?click_id=568579886747811842&ppc=0
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