The county of Rutland was not fully formed in 1086. Part of the later county was included in Northamptonshire. In addition, Rutland was treated as an appendage to Nottinghamshire for certain purposes while some of its manors were intermixed with holdings in Lincolnshire.
See Charles Phythian-Adams, 'The emergence of Rutland and the making of the realm', Rutland Record, vol. 1 (1980), pages 5-12.