Many arrived on Sunday though some were in place along the Mall as early as Saturday.
Nurse Sue Grave, 53, from Chester said she expects the funeral to be “overwhelming and so emotional”.
Ms Grave, who previously camped out to celebrate the platinum jubilee as well as other royal events, said: “I am ex-forces. She was our commander-in-chief. I have just always been a royalist.
“People from every culture and country have been walking by here and she has done so much for not just our country, but the Commonwealth and the world.
She said: “I need to see her so that I can feel she can go off and rest in peace now. I guess it is closure. Sleeping here was very cold but the amount of services and helpers have been amazing.
“St John Ambulance have given us foil sheets to keep us warm. We can get tea and coffee. The nearby toilets are being cleaned constantly. The police have brought us food.
“Everyone, including the security, are just checking in on us to see that we are OK. We have managed to build a community in such a short space of time.”
Nurse Gwenda Griffiths, 66, of Swansea, South Wales, quickly made friends with Ms Grave after arriving on Saturday.
She said: “The Queen was a very special person to so many people – not just our generation but all generations across the UK. This is just my way of honouring her.”
Margaret Ford, 76, a retired decorator and designer from Llandaff North, Cardiff, Wales, said: “I find it a privilege and an honour to do this. It is no time at all really and it is all to do with caring about people.”
She said: “The Queen was God fearing. She was caring and loving. I would say she was gentle as well.
“It is worth it. It is lovely, the atmosphere, the respect and to be able to thank royalty for what they have done and for what they will do, I believe.”
She said she remembered how solemn the Queen Mother’s funeral was in 2002 when she travelled to London for the event.
She recalled: “All I could hear was the horses hooves and the men walking. It was amazing. It was so dignified.”
Mrs Ford said she felt “quite sure” she will be “tearful at times” on Monday, but said there would also be “lovely music as well to enjoy”.
Late-Night rehearsal held for Funeral of HM Queen Elizabeth II
The early arrivals will be joined by many more mourners with Transport for London (TfL) preparing for around one million people to visit the capital.
Around 250 extra rail services will run – including some overnight trains – and National Highways has suspended planned motorway closures across England.
There are fears the transport network will be overwhelmed on Monday afternoon if too many people travel home immediately after the funeral procession leaves Westminster shortly after noon.
Mourners are being urged to delay their return journeys and check for travel updates.