Around 10 caravans moved on to land off Dunston Road on Wednesday afternoon.
A source told the Derbyshire Times: "They're in the car park behind the very recently vacated AIG building at the entrance to Millennium Way and there's also a caravan parked on grass half way up the driveway leading up to East Midlands Chamber.
"They are all sharing a single outside tap on the building that, despite the property being vacated, hasn't been shut off.
"They're hidden from the road by the bushes just beyond the Dunston Innovation Centre."
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If Gypsies or Travellers are camped on council-owned land, the council can evict them.
However, if the encampment is on private land, it is usually the landowner's responsibility.
The Derbyshire Times is making attempts to find out who the landowner is so we can approach them for a comment about the situation.
Cost of illegal Traveller camps revealed
More than £10,000 of taxpayers' cash was spent on dealing with illegal Gypsy and Traveller camps last year.
Figures obtained under the Freedom of Information Act (FOI) show Chesterfield Borough Council shelled out £10,838.34 after Gypsies and Travellers illicitly set up camp in seven separate locations during 2018.
Councillor Chris Ludlow, Chesterfield Borough Council's cabinet member for health and wellbeing, said: "In the last year, the council spent more than £10,000 in removing Gypsies and Travellers from illegal sites.
"This is money paid in council tax by our residents and, given that the council has lost more than half the funding it receives from the Government since 2010, this could be better spent elsewhere on the services we provide.
"We work closely with the police and other agencies and will continue to react quickly when faced with illegal encampments to make sure they are moved on as quickly as possible and so our facilities can remain open to the public."
In February, the council granted conditional planning permission for a Traveller site with three pitches on land to the rear of Mayfields at Hady Lane, Hady.
The planning consent means a requirement for the council to identify sites for two permanent Gypsy and Traveller pitches as part of its latest Local Plan has now been met.
Police to be given more powers to crackdown on illegal Traveller sites under new plans
Police will be given strengthened powers to crackdown on illegal Traveller sites under new Government plans.
Home Secretary Sajid Javid said unauthorised camps can cause settled communities 'significant distress'.
Last year ministers launched a consultation on the effectiveness of enforcement against unauthorised developments and encampments.
Mr Javid said: "The vast majority of Travellers are law-abiding citizens - but illegal sites often give an unfair, negative image of their community and cause distress and misery to those who live nearby.
"There is a widespread perception that the law does not apply to Travellers and that is deeply troubling.
"The result of our initial consultation was clear - people want to see greater protection for local communities and for the police to be given greater power to crackdown on trespassers."
Mr Javid will also consider making it a criminal offence to set up such camps. It is currently defined in law as trespassing, a civil matter.
Communities Secretary James Brokenshire added: "During our consultation, we have heard accounts of needless and unacceptable noise, abusive and threatening behaviour and extensive litter and waste from illegal traveller sites.
"Only a small minority of people are causing this distress, but it’s right that police are given extra powers to step in.
"We are committed to working with councils to help them deal with these challenging cases, while also ensuring travellers have good access to legal sites."
Under the proposals, which will be subject to a further consultation, amendments would be made to the relevant sections of the Criminal Justice and Public Order Act 1994 to:
• Permit police to direct trespassers to suitable authorised sites located in neighbouring local authority areas
• Increase the period of time in which trespassers directed from land would be unable to return from three months to 12 months
• Reduce the number of vehicles needing to be involved in an unauthorised camp before police powers can be exercised from the current six or more down to two or more
• Enable the police to remove trespassers from land which forms part of the highway