The symbolic gesture means the group has made a Unilateral Declaration of Independence which means Southend Council's contraversial plans for Priory Crescent could not go ahead without their permission, they claim.
Protest leaders are concerned the proposals could mean the removal of up to 100 trees from the park or land legally associated with it.
The declaration echoes the situation in the 1960s when the African country of Rhodesia was declared independent and shed its colonial shackles under the Wilson Government.
Campaigner Chris Ford said: "We kept the campaign under wraps until the last minute because we knew the council would move heaven and earth to stop us setting up our tents.
"We are not happy with the council, who were elected by a minority, because they are being undemocratic and need to listen to the 25,000 people who are opposing to the project.
"There are about 121 beautiful trees that are set to have a chain saw right through them. There are far greater people against these plans than would support them and there is a lot of community support for our campaign."
Following the campaign residents feel they can make a difference to the plans and hope they will have their concerns listened to by council officials.
Mr Ford said: "We are casting the net and are trying to get people further afield to notice us. We want to add strength and support to the scheme and we want to let the council know we are not going to go away."
Roger Weaver, Southend Council's executive councillor for planning, transportation and engineering, said: "We do listen on a regular basis to the views of the Priory Park protesters. We were aware of the actions of the protesters at the weekend and I personally observed the group as they camped out on the site.
"But this is a democratic society and despite this being public land we felt it would be inappropriate if we interfered with their vigil."
He added: "At all the times the council has responded to the protest group's questions and actions but we believe now it is time for the silent majority to be heard.
"The regeneration of Southend has to be a priority for the town."