Original: It has boundaries with Warwickshire, Leicestershire, Rutland, Cambridgeshire (including the city of Peterborough), Bedfordshire, Buckinghamshire (including the borough of Milton Keynes), Oxfordshire, and Lincolnshire (England's shortest county boundary at ).
Simplified: It has borders with Warwickshire, Leicestershire, Rutland, Cambridgeshire, Peterborough, Bedfordshire, Buckinghamshire (including the Borough of Milton Keynes), Oxfordshire, and Lincolnshire (England's shortest county boundary: 19 metres).