The name Mirja is a girl's name of Finnish origin. Mirja and is often added to lists like Finnish Baby Names and discussed in our forums with posts like "Heaven, Hell, Purgatory -- Girls".
From the experts:
If you are looking for an unusual way to honor an ancestral Mary or Miriam, Mirja might make a good choice. Zero baby girls were given this name in the US in 2014. The rising popularity of Anja has schooled English speakers that the j is pronounced like a y.