Yes, retirement income is taxable to North Dakota. There are exclusions for retirement income for Railroad Retirement Board, Military Retirement Benefits and Licensed Peace Officers.
What about retirement from the Railroad Retirement Board?
North Dakota does allow for a subtraction on retirement income if the benefits are from the U.S. Railroad Retirement Board.
The taxable amount entered on the federal return for box 7a of form 1099-RRB, is automatically subtracted from your North Dakota taxable income.