I asked another collector who is authoritative on these helmets. He believes that it is a Hesse-Darmstadt schlossgarde or palace guard helmet but more research is needed to confirm 100%. Thank you Amy, I've really enjoyed researching your helmet and learned a lot about these that I didn't know. I've attached a painting of Grossherzog Ludwig III 1806-1877. The portrait is from 1857 just eight years after this model helmet was introduced. Here's a link to some information on the palace of the grand dukes.
https://en.wikipedia.org/wiki/Residential_Palace_Darmstadt. Also here are helmets I collect from this period. They are very hard to find but I love this history so I also research it with 70 mm zinnfiguren toy soldiers of the armies from the period recast from the original molds as well. Many "lost" early molds were rediscovered in former East Germany after unification so its essentially a new field.