The3Million, which campaigns for EU citizens' rights, says it is concerned for the hundreds of thousands of people still waiting to find out if they can continue living in a post-Brexit UK.
Home Office data shows 9,650 EU citizens had successfully applied to continue living in Mansfield by June 30 – the deadline for new applications imposed by the Government following Brexit.
A further 3,930 had successfully applied to continue living in Ashfield, as well as 5,830 in Newark & Sherwood..
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EU citizens with limited reasonable grounds for missing the June deadline can still apply to secure their rights.
Those who have lived in the UK for five years and meet the criteria, can receive settled status and remain in the country indefinitely.
Others who have lived in the country for less time can receive pre-settled status, which allows them to remain for a further five years. They can later apply for settled status.
Some citizens not from the European Economic Area may also qualify for the scheme, for example if they are family members of EU citizens living in the UK.
Between the launch of the scheme and the deadline, a total of 10,220 applications were dealt with in Mansfield, with 5,790 people granted settled status and 3,860 pre-settled status.
About 570 applications were either refused, withdrawn, or invalid.
The highest number of applications received came from Poland, at 4,760, followed by 3,330 from Romania and 1,400 from Latvia.
In Ashfield, a total of 4,090 applications were dealt with, with 2,660 people granted settled status, 1,270 pre-settled status and about 160 applications refused, withdrawn, or invalid. The highest number again came from Poland, at 1,720, followed by 900 from Romania and 340 from Latvia.
In Newark & Sherwood, 6,090 applications were dealt with, with 3,790 people given settled status, 2,040 pre-settled status and about 260 refused, withdrawn, or invalid. Applications from Poland nationals was again the highest, at 2,180, followed by 1,610 from Romania and 1,160 from Lithuania.
The3Million said, although millions of applications had been processed under the EU Settlement Scheme, almost half a million people were still awaiting a decision.
A spokesman said: "This backlog is unlikely to be cleared anytime soon, given the slowing pace of decision making.
“The scheme will also continue to receive new applications from vulnerable citizens who missed the deadline, as well as those upgrading from pre-settled to settled status and from joining family members.
“It is therefore crucial the Government commits to a long-term plan to support all applicants."
The Government said those who applied to the scheme by the June deadline, but have not had a decision, have their rights protected until their application is decided.
Kevin Foster, minister for future borders and immigration, said: “I’m delighted thousands more people have been rightly granted status through the hugely successful EU Settlement Scheme.
“We continue to work as quickly as possible to conclude applications, as well as supporting people with their late applications.
“Our message remains clear. The Home Office is looking for reasons to grant status rather than refuse. I would encourage anyone eligible who is yet to apply to get in touch and join the millions who have already secured their rights.”