Acamar, also known as Theta Eridani, was the primary of the Acamar system, in the Beta Quadrant. It was located near Adelphous, Carraya, and the Epsilon Outposts. (DIS: "Choose Your Pain")
In 2256, this star's location was labeled on the star chart "Alpha/Beta Quadrant Overview" in the ready room aboard the USS Discovery. (DIS: "Magic to Make the Sanest Man Go Mad")
In 2257, during the Federation-Klingon War, this star's system was occupied by the Klingons. (DIS: "The War Without, The War Within")
In 2399, the location of Acamar was labeled on a star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters. (PIC: "Maps and Legends")
This star was only mentioned in writing.
In the Star Trek: Star Charts (p. 56) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Acamar was identified as a multi-star with a pair of A-class stars.
At StarTrek.com, this star was located 50-60 light years from Sol.
Furthermore, at StarTrek.com, this star was located in the Mempa sector in the Beta Quadrant.