Jackson was appointed Lincoln boss in October 2007
League Two side Lincoln City have sacked manager Peter Jackson and his assistant Iffy Onuora.
Chairman Steff Wright told BBC Radio Lincolnshire: "It's always a difficult decision, but it's a calm and collected one the board has made.
"You must look back over 12 months and you've got to see a pattern of progression over a period of time."
First-team coach Simon Clark and head of youth Tom Spall have been placed in temporary charge at Sincil Bank.
"Last season was a frustrating season. Our home form was very disappointing and that ended up in a reduction of gates," Wright added.
Former Huddersfield boss Jackson was named as boss of the Imps in October 2007 following the sacking of John Schofield.
At the time, City were bottom of League Two, but Jackson guided them to safety and a 15th-placed finish, despite taking time off to undergo treatment for throat cancer.
However, Jackson was unable to significantly improve City's fortunes in the following campaign, with his side managing just six home wins on the way to a 13th-placed finish in the bottom tier of the Football League.
A series of mixed results at the beginning of this season began with a 1-0 win at home to Barnet on the opening day but was followed by a League Cup first round exit to Barnsley at Sincil Bank and a 1-0 defeat away at Accrington.
A 2-0 win at Bradford would prove to be the last time that Jackson tasted victory as Lincoln manager, as the supporters turned on him with a chorus of boos following the 2-0 defeat at home by Burton Albion.
"The record I have got here [at Sincil Bank] is not the best so I expect the criticism," Jackson told BBC Radio Lincolnshire after that game.
The Imps went down to a 3-0 defeat at league leaders Dagenham & Redbridge on Saturday, with Tuesday's 1-0 loss away to Darlington in the first round of the Football League Trophy proving to be Jackson's final game in charge.
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