The results are expected to be out by afternoon.
Security personnel have been deployed outside the vote counting centres.
Over 73.45 percent voter turnout was recorded on December 21.
The voting at 258 polling stations took place peacefully under heavy security, which included 2,500 state police personnel and 15 companies of Central Armed Police Forces guarding the centres.
About 1,638 election officers manned the poll process.
Chief Minister K Palaniswami and Deputy Chief Minister O Pannerselvam, DMK working president M K Stalin and sidelined DMK leader TTV Dinakaran had left no stones unturned to ensure victory for their respective candidates.
The by-poll was earlier scheduled for April 12 but was cancelled following allegations that sums of money were distributed by the faction of jailed All India Anna Dravida Munnetra Kazhagam (AIADMK) leader VK Sasikala in a vote-for-cash scam. (ANI)