Counting is under way in the parliamentary by-election triggered when an MP quit amid claims he mocked victims of the Northern Ireland Troubles.
Sinn Fein's Barry McElduff resigned as West Tyrone MP in January, 10 days after a controversy flared when he posted a video of himself with a Kingsmill-branded loaf on his head on the anniversary of the notorious Kingsmill massacre.
He insisted the video was not an intentional reference to the 1976 sectarian murders of 10 Protestant workmen by republican paramilitaries near the Co Armagh village of Kingsmill, but he acknowledged it had caused hurt and offence to victims' families.
Five candidates are contesting the subsequent by-election.
Polls opened at 7am and closed at 10pm.
There was a security incident during the day when a man was arrested on suspicion of possessing a firearm at a polling station.
Police investigating the incident in Greencastle, Co Tyrone, detained the 59-year-old on suspicion of possession with "intent to cause fear or alarm".
The first ballot boxes were opened at the count centre at Omagh Leisure Centre at around 10.15pm. The count is set to extend into the night.
Sinn Fein's Orfhlaith Begley is defending a 10,000-plus majority in a seat where the party took just over 50% of votes cast in last year's general election.
It would be a seismic shock if the abstentionist 26-year-old solicitor, a political newcomer, did not win a seat the republican party has held for 17 years.
Thomas Buchanan is contesting the seat for the Democratic Unionists.
The Assembly member - who is the only candidate not aged in his twenties - managed just over half the number of votes notched by Sinn Fein when he ran in last year's general election.
Assembly member and law graduate Daniel McCrossan, 29, is running for the SDLP while local councillor Chris Smyth is representing the Ulster Unionists.
Stephen Donnelly is the Alliance Party's candidate.
Given the circumstances around Mr McElduff's departure, issues affecting victims of the Troubles have been a key feature of what has been a relatively low-key campaign.
Kevin Skelton, whose wife was killed in the 1998 Omagh bomb, put himself forward as a potential victims unity candidate, asking the other parties to unify behind him in a bid to defeat Sinn Fein.
He failed to secure the necessary cross-party support and did not end up putting his name on the ballot.
Unsurprisingly Brexit has also featured on the campaign trail in a constituency whose western boundary runs along the Irish border.
The ongoing referendum campaign in the Irish Republic on the state's restrictive legal framework on abortion has undoubtedly also had an impact on the dynamic of the by-election debate north of the border.
The candidates' position on the emotive issue has been subjected to greater scrutiny than they might have expected.