It was customary up to the 20th century to say "the county of Lincoln" - the term Lincolnshire was not generally used. The county of Lincoln was split up into three "parts" until 1974 when local government reorganisation took place. The three "parts" were Lindsey, Kesteven and Holland. Each had its own Quarter Sessions.
There are 14 registration districts covering Lincolnshire (for census). Some registration districts cover parts of other counties: some of Rutland is in Stamford RD, a few Leicestershire parishes are in Grantham RD, a few Nottinghamshire parishes are in Gainsborough RD. Some Lincolnshire parishes are in Newark (Nottinghamshire) RD, others are in Thorne and Goole RDs (West Yorkshire) and Crowland is in Peterborough RD (Northamptonshire); county boundaries are not followed by the registration districts.
There are 23 Deaneries in Lincolnshire. These are ecclesiastical boundaries and the marriage indexes are published in Deaneries.
There are 32 Wapentakes (called "Hundreds" in other parts of England) in Lincolnshire. These are ancient political collections of parishes which had lost much meaning by the 1700s.
This is all very confusing which is why The Lincolnshire Family History Society publishes the "Gazetteer of Historic Lincolnshire for Family & Local Historians". All the different boundaries are explained in this book which also lists all the parishes, townships, hamlets, even some large houses and other very small areas. From this book you can also find out in which Wapentake, Methodist Circuit, Poor Law Union, Registration District, Registration Sub District, Deanery etc. each place is in. You can also find out whether the Protestation Returns are extant and find the grid reference for each place. If everyone researching in Lincolnshire had the Gazetteer, no one would need to ask where this place or that place is; you would have the information at your fingertips.