Five candidates are in the fray including Shiv Sena's Amit Ghoda, Congress leader and former minister Rajendra Gavit and MNS's Manisha Nimkar.
The polling was peaceful, said the district authorities.
A Shiv Sena worker from Thane city, Madhukar Kadam (52) died in Dahanu after suffering a massive cardiac arrest, party sources said. Kadam had been campaigning for Amit for the past one week.
The byelection was necessitated by the death of sitting MLA Krishna Ghoda of Shiv Sena. Ghoda, Amit's father, passed away last May.