Police have said there are no excuses for breaching Covid-19 laws after being called to break up a 200-strong gathering at a university hall of residence.
Investigations are ongoing into the incident, after officers were called to a courtyard at the student block in Nottingham.
Police said partygoers across Nottinghamshire had their evenings "interrupted" on Saturday, as officers tackled several illegal gatherings and issued multiple fines.
The force said in a statement that officers were called to a flat in Pilcher Gate, Nottingham, shortly before 10.30pm and issued £200 fixed penalty notices to 21 people found inside.
"Investigations are ongoing to establish the identity of the organiser, who could face additional punishment," police said.
"Another large party was broken up shortly after midnight at an address in Corporation Oaks, St Ann's, and the organiser was issued with a summons to appear in court at a later date."
Elsewhere in the county, officers issued another five £200 fixed penalty notices after responding to reports of a party in a field in Gonalston, near Lowdham, shortly after 9pm.
Investigations are under way to identify the organiser of the event, and a driver who crashed into a police car as they fled the scene.
The force statement added: "Investigations are also ongoing after officers dispersed a gathering of around 200 young people in an outdoor courtyard at a student halls of residence in St Peter's Street, Nottingham."
Detective Superintendent Andrew Gowan said: "The very last thing we want to be doing as police officers is to be punishing people for gathering together and having fun.
"However, the current national restrictions are in place to protect the wider public from harm and we will keep enforcing them for as long as we need to.
"Whilst it is heartening that the vast majority of people clearly understand and are obeying the current restrictions, it is deeply disappointing that so many others needed such an expensive reminder that the rules apply equally to everyone.
"We understand that this is a difficult time but there really are no excuses for this kind of behaviour where people are blatantly ignoring the restrictions in such large numbers."