UKIP gained five seats on Castle Point Council including leader Pam Challis' St Peter's ward to remove the Conservatives from overall control.
The Tories remain the largest party, but will have to elect a new leader and decide whether to form a coalition or try to rule as a minority administration in the next few days.
Mrs Challis lost her seat to 87-year-old Ron Hurrell, who was said to be at home in bed, rather than at the count.
Ukip parliamentary candidate Jamie Huntman said: "Lots of people came out to vote for us who hadn't voted for years and years, they've got someone who speaks for them now rather than the three centre left parties."
Heartbroken Mrs Challis said: "I'm proud of what I've achieved over the years I can go out with flying colours, having turned the council from a poor council into one that's recognised across the country as being a good one."
The council now has 20 Conservative members, 16 Canvey Island Independents and 5 Ukip members.
Ukip gained members in Appleton, Victoria, Cedar Hall, St Peter's and St George's.
The Canvey Island Independents re-gained the Canvey Island South seat they previously lost to a defection. Successfully defending five other seats.
For much more election coverage, see Monday's Castle Point Echo.