Gillian Merron had held the seat since 1997
The Conservatives have gained Lincoln from Labour and taken control of the whole county.
Former public health minister Gillian Merron was 1,058 votes behind Karl McCartney who took 17,163 votes.
Ms Merron had held the seat since 1997 but saw a 5.9% swing from Labour to the Conservatives.
The Tories held South Holland & The Deepings, Boston & Skegness, Grantham & Stamford, Gainsborough, Sleaford & North Hykeham and Louth & Horncastle.
In Grantham and Stamford, Nicholas Boles gained 26,553 votes taking over from the former Conservative MP Quentin Davies who defected to Labour in 2007.
Mark Simmonds retained his Boston and Skegness seat with 21,325 votes gaining a 49.4% share.
Boston & Skegness - 61.1%
Gainsborough - 68.3%
Grantham & Stamford - 68%
Lincoln - 62.2%
Louth & Horncastle - 65%
Sleaford & North Hykeham - 69.6%
South Holland & The Deepings - 65.8%
He has seen his majority increase by just over 3% from the 2005 election.
Edward Leigh took 24,266 votes for the Tories in Gainsborough - with Pat O'Connor gaining 13,707 for the Lib Dems.
John Hayes won more than three times as many votes as his nearest rival in South Holland & The Deepings with 29,639 votes - Jennifer Conroy won 7,759 for the Lib Dems.
In Louth & Horncastle Peter Tapsell got 25,065 votes - ahead of the Lib Dems' Fiona Martin on 11,194.
Stephen Phillips took 30,179 votes for the Tories in Sleaford & North Hykeham with David Harding-Price got 10,814 for the Liberal Democrats.