The elections in Assam, which began on April 3, kicked off a month-long poll process in five states in India's south and east.
Officials said turnout reached around 65% of the 8.2 million registered voters in Assam, the biggest state in India's isolated northeast, despite heavy rain.
The senior election officer in Guwahati said: "For the first time in many years the election process ended in such a peaceful manner in Assam. It is really a record."
Police said unidentified militants threw an improvised bomb at a vehicle carrying paramilitary troops in the remote Karbi Anglong district, injuring two of the passengers.
But otherwise they said voting had passed off peacefully.
Monday's polling concluded elections in Assam, but results will be announced only after polls in the other states are completed early next month.
The Congress party rules three of the five states facing polls and heads the federal government. Congress and its allies are fighting stiff battles against the national coalition's own communist allies as well as regional opposition parties.
"For the first time in many years the election process ended in such a peaceful manner in Assam. It is really a record"
Senior election officer
Assam - ruled by the Congress - is home to ancient tribes but is plagued by insurgencies against Indian rule and previous elections have been marred by rebel attacks on candidates, political workers and civilians.
The Congress government in Assam is fighting for re-election against a regional opposition party and the Hindu-nationalist Bharatiya Janata Party (BJP), India's main opposition party.
The other states voting are southern Tamil Nadu and Kerala as well as the federal enclave of Pondicherry and communist-ruled West Bengal in the east.