The 58-year-old moved from his position as chief executive to director of football earlier this year.
Spireites director Ashley Carson said the role was now "redundant".
Turner, who joined Chesterfield in 2011, told the club website: "I am very disappointed to be leaving Chesterfield, but I can understand the situation and I leave on good terms."

Shiv Kumar Yadav has also been charged with "criminal intimidation" of the 26-year-old woman, reports said.
The victim had used the Uber smartphone app to book a taxi home but said she was taken to a secluded area and raped.
Delhi later banned Uber and several other web-based taxi firms for failing to carry out adequate driver checks.
Although the driver has not yet given a statement in public, police say he has confessed to the crime. They say he has also been identified by the victim.
Rape and the issue of sexual violence against Indian women have been in the spotlight in recent years ever since a 23-year-old physiotherapy student was gang-raped and murdered in Delhi in December 2012.
The crime prompted global outrage and a tightening of the laws on sexual violence, but correspondents say they have failed to act as a deterrent.
Earlier this month, five men were arrested in Calcutta for kidnapping and repeatedly raping a Japanese student.
And in the northern Indian state of Uttar Pradesh, two policemen were arrested for allegedly abducting and raping a teenager.

Mr Tucker will take over on 1 October, succeeding Douglas Flint who has been in the role since 2010.
The appointment breaks an HSBC tradition of appointing insiders to the chairmanship.
One of his first jobs will be to find a replacement for Stuart Gulliver, the chief executive of HSBC, who plans to step down next year.
While HSBC is Europe's biggest bank, the bulk of its profits are generated in Asia.
Mr Tucker has been chief executive of AIA for seven years, during which he oversaw the insurer's expansion in Asia.
Before AIA, he was the chief executive of insurance giant Prudential, and brings to HSBC his experience at the top of a UK financial giant as well as his Asian exposure.
Richard Dunbar of Aberdeen Asset Management, told the BBC the bank has "obviously decided" that an external perspective would be useful to HSBC at this time.
He added that while chief executive of Prudential, Mr Tucker did a good job of expanding its Asian assets, which are seen as the firm's "jewel in the crown".
HSBC has been through an overhaul in recent years in an attempt to reverse declining profits.
Over the past six years it has cut more than 40,000 jobs and sold off businesses.
Despite those efforts, profits tumbled more than 60% last year.
The banking industry has been hampered by the extended period of very low interest rates, which makes lending money less profitable.
For HSBC, that problem has been compounded by its move into less risky areas of banking since the financial crisis which started in 2007.
Those challenges make the appointment of a new chief executive even more crucial for investors, a search which will now be led by Mr Tucker.
HSBC has also been attempting to repair its image after a series of scandals.
Earlier this year it reached a $470m (Â£325m) settlement with the US government and states related to dubious mortgage lending and foreclosure practices during the financial crisis.
In 2015 Mr Gulliver and Mr Flint apologised for "unacceptable" practices at its Swiss private bank which helped clients to avoid tax.
In late 2012 HSBC paid US authorities $1.9bn in a settlement over money laundering.
AIA said that Ng Keng Hooi, would take over as chief executive from 1 September.
Chesterfield director of football Chris Turner has left the struggling League One club.
[NEXT_CONCEPT]
A court in the Indian capital has formally charged a driver of the Uber web-based taxi firm with the rape and kidnapping of a passenger last month.
[NEXT_CONCEPT]
HSBC has appointed Mark Tucker, the chief executive of Asian insurer AIA, as group chairman.