Elizabeth Hart - known as Bonnie - has pledged to improve the county's image in the wider world and help work to develop business and commerce
Mrs Hart, who lives in Hockley and represents Rochford West division, is the first south Essex councillor to become chairman since Labour's Ron Kennedy from Southend held the office in the mid-Nineties.
She said: "I am absolutely thrilled. What has been so nice is everyone from all sides of the council chamber has given their congratulations.
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"I never thought when I was first elected 13 years ago that I would finish up as chairman.
"I want to make developing business in Essex as my theme for the coming year as I believe people have the wrong Essex girl and Essex man image of the county.
"It's a wonderful place with a lot of potential and should be the county of choice for business and pleasure."
Mrs Hart is no stranger to presiding over council meetings. She chaired Rochford District Council in the early Nineties.
Much of her role will be civic and ceremonial.
County council leader Lord Hanningfield said: "Bonnie Hart has been a passionate representative of Essex for a number of years and I am sure she will do a wonderful job as chairman."
The new vice-chairman is one-time highways supremo Rodney Bass - best known as the man who turned out the county's streetlights after midnight.
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