This installment of where to start is adult historical fiction. As with the YA version, I'm not including historical fantasy, or alternate history/steampunkish sort of things. Those genres will be getting their own where to start. This is just regular historical fiction that is not considered YA. Also there will be no time travel, so nothing like Outlander will be on here.
Some Staples in the genre you should probably try first:
Philippa Gregory-She's written dozens of historical fiction series. The Tudor Court series is probably her most well known (that's the one that has The Other Boleyn Girl in it)
Girl With a Pearl Earring by Tracy Chevalier
Pillars of the Earth series by Ken Follet
Atonement by Ian McEwan
Aubrey and Maturin series by Patrick O'Brien (you've probably heard of the first book: Master and Commander)
Some current popular titles you'll likely hear about first:
All the Light We Cannot See by Anthony Doerr
Lisa See-Snow Flower and the Secret Fan is probably her most popular, but she has a few historical books out there.
The Paris Wife by Paula McLain
Thomas Cromwell Trilogy by Hilary Mantel (you probably know the first book: Wolf Hall)
Sarah Waters-Her most popular is probably Fingersmith.
Some random popular titles:
Cold Mountain by Charles Frazier
The Poisonwood Bible by Barbara Kingsolver
Melanie Benjamin-Would start with The Aviator's Wife.