The former England player opened the batting and made 101, with nine fours, before he was stumped off Ashar Zaidi.
Laurie Evans provided late impetus with an unbeaten 70 off 53 balls as they posted a total of 283-7 at Edgbaston.
Tom Westley made 61 for Essex and Ryan ten Doeschate was last to go for 50 as they were all out for 213.
It was a disappointing batting effort which left 7.5 overs unused, and Warwickshire will now be at home to Somerset - who beat Worcestershire by nine wickets - on 28 or 29 August, with a place in the Lord's final at stake.
With England seamer Chris Woakes conceding 47 from seven wicketless overs, it was Warwickshire's spinners who undermined the Essex run chase after openers Westley and Nick Browne put on 75 in 12 overs, claiming eight wickets between them.
Browne was stumped off Ateeq Javid and Jesse Ryder, Jaik Mickleburgh and Zaidi were all guilty of poor shots as numbers three to six in the order all failed to reach double figures.
Essex slumped to 134-6 in the 28th over, with leg-spinner Josh Poysden claiming 3-46, and it was Jeetan Patel (3-32) who ended the game by having ten Doeschate lbw after he reached a run-a-ball half-century.
Earlier Trott, who now averages 77.80 in this season's competition, anchored the Warwickshire innings after skipper Ian Bell was caught behind for a fourth-ball duck.
He shared a stand of 136 with Tim Ambrose (60) and although his dismissal sparked a mini-slump from 227-3 to 257-7, Evans hit three sixes and three fours to boost the total in the closing overs.

The charity said this was disproportionate to the sector's size, which is 13% of housing in Scotland.
Homeless applications have decreased by a third in the past five years but the Shelter said the statistics did not tell the full story.
It said it was important that vulnerable households were supported before they were pushed into crisis.
According to the latest Scottish government figures, the proportion of  homeless applications that come from the private rental tenants rose from 13% 2008-09 to 18% in 2013-14.
However overall homelessness in Scotland fell by 34% during the same period, official statistics showed.
Graeme Brown, director of Shelter Scotland, said: "Whilst the headline figures show that homelessness applications are down by one third in the last five years, which is welcome, our analysis shows it is not all good news for homeless people in Scotland.
"The 36,457 households making homeless applications, a youth homelessness rate at 13.7 per 1,000 and a rising proportion of homeless applications from the private rented sector signal that, although there are movements in the right direction, there is still a long way to go."
"With the significant weakening of the welfare state in recent years, it is more important than ever to ensure that vulnerable households are offered support before they are pushed into crisis."
The report, 'Homelessness in Scotland 2014: Getting Behind the Statistics', has been released ahead of Shelter Scotland's annual conference later this month.
Housing minister Margaret Burgess said: "Homelessness in Scotland is falling and the number of homeless applications from the private rented sector has actually fallen by 21% since 2008/09.
"The Scottish government is working closely with local authorities and their partners, and with Shelter, to prevent homelessness, increase the number of affordable homes and address the issue of empty homes. Where people do become homeless, our focus is on finding the best outcomes."
Jonathan Trott made his third One-Day Cup century in four innings as Warwickshire reached the semi-finals with a 70-run home win over Essex.
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Almost a fifth of homeless applications now come from the private rented sector, according to Shelter Scotland.