Figured it out. I was being an idiot and not escaping the ‘\’ before the v11.0.
Thanks all!
openCon = new SqlConnection("Data Source=(LocalDB)\\v11.0;" +
"AttachDbFilename=" + AppDomain.CurrentDomain.BaseDirectory + "Encounter.mdf;" +
"Integrated Security=True");
solved How to connect to SQL Server database file in my solution [closed]