Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Traill County is a county located in the U.S. state of North Dakota. Current estimates place the 2008 population at 7,820; the 2000 census listed the population at 8,477. Its county seat is Hillsboro, and its largest city is Mayville.Traill County was created in 1875 by the 1874-75 territorial legislature. It was named after Walter John Strickland Traill, an employee of the Hudson''s Bay Company and son of Canadian pioneer Catharine Parr Traill.