St Albans Tory councillor Keith Stammers lost out to Lib Dem Judith Shardlow after their votes were tied at 1131 each after three recounts.
The election saw the Lib Dems take back power at St Albans after losing it to no overall control in 1999.
Lib Dem David Poor, who won the Sopwell seat from Labour, welcomed the result.
Mayor re-elected
"Tonight has been an excellent night. It is excellent work by all the Lib Dems," he said.
The party also retained control of Three Rivers District Council in Rickmansworth.
But there was bad news for the Lib Dems in Milton Keynes where the council went to no overall control.
The Tory Party kept control of North Hertfordshire, Broxbourne, South Bedfordshire, Welwyn Hatfield and Hertsmere councils.
Bedford council stayed with no party in overall control. The election saw Labour group leader and deputy mayor Shan Hunt beaten in her ward of Kempton South by the Conservative Jasbir Singh Parmar.
In Watford, Lib Dem Dorothy Thornhill was re-elected Mayor of Watford at the first count.
Votes for the Watford council are not being counted until Friday.
Labour has held onto control of Stevenage council.
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