This year, a new biometric identification system was set up that requires voters to verify their identity and registration using a fingerprint reader that often needs several tries before it works.
With high expectations from botth the local and worldwide communities for a peaceful election, former United States of America president Barack Obama was among the first to send their well wishes to Kenyans, as well as a message to Uhuru and Raila.
Their votes will matter in some of the most contested parts of the country.
A key concern is whether Kenya will echo its 2013 election, a mostly peaceful affair despite opposition allegations of vote-tampering, or the 2007 election, which led to violence fueled by ethnic divisions that killed more than 1,000 people.
EAT (2100GMT on Monday) to vote in what many are terming as game-changing elections as incumbent President Uhuru Kenyatta, a businessman and son of Kenya's founding father Jomo Kenyatta faces off with Raila Amollo Odinga who has tried to become president four times in the past but has never emerged victorious. "I am willing myself to accept the will of the people, so let them too", he said as he voted at the Mutomo Primary School in Gatundu, his home turf.
President Barack Obama speaks during a news conference with Kenyan President Uhuru Kenyatta at the State House in Nairobi, Kenya, July 25, 2015.
Political and ethnic tensions exploded into bloodshed after Odinga - who lost to then-President Mwai Kibaki - claimed the election was rigged.
"There are a lot of people in line, and it is going to take some time, and we are going to need to be very patient", said Kerry, chief election observer for The Carter Center.
The victor needs one vote more than 50 percent, and to win at least a quarter of the vote in 24 of Kenya's 47 counties.
Opinion polls suggested Kenyatta and Odinga, who is fighting his fourth presidential election, are neck-and-neck, leading many Kenyans to fear a disputed result and possible violence. This time around the stakes are higher, and many fear a repeat of the post-election violence a decade ago.
Kenyatta and Odinga originate from opposing tribes.
Odinga, 72, is also a member of Kenya's political elite. As many as 180,000 police officers have been deployed across the country to prevent violence.
Odinga told the European Parliamentarians observing the elections that his party, the National Super Alliance (NASA) was concerned about the integrity of the voters register, the reference point for tomorrow's vote.
Polls in Kenya have officially closed, but thousands remain in queues to cast their ballots in a presidential election that has been marred by claims of vote rigging.
In the capital Nairobi, voters continue to trickle into the polling stations. It was still early, he said, but what has been tricky historically in Kenya is the counting.
Former U.S. Secretary of State John Kerry is among worldwide observers who will be monitoring the election.