Sean Dyche's side have now won four of their last five league matches, remaining unbeaten in the process, with the result leaving them 15th in the table on 40 points.
Doucoure headed the winner in the 31st minute, with Sheffield United suffering their 27th loss of the campaign, while they have now conceded 101 times in the Premier League this season.
Everton have won each of their last five league games at Goodison Park, keeping clean sheets in all of those fixtures, and the Merseyside outfit will now be bidding to finish their campaign with a positive result against Arsenal next weekend.
Sheffield United, meanwhile, will end what has been a difficult season at home to Tottenham Hotspur.
Everton's excellent run of form continues
Doucoure should have sent Everton ahead in the early stages after smart work from Dominic Calvert-Lewin, but the midfielder saw his effort kept out by Sheffield United goalkeeper Wes Foderingham.
The Toffees were the team on the front foot, but Sheffield United were having their moments, with Cameron Archer curling just past the post from a wide angle.
Everton made the breakthrough in the 31st minute through Doucoure, who headed a cross from Calvert-Lewin into the back of the net from close range.
VAR had a look at an incident involving Jack Robinson and Calvert-Lewin late in the first period, with the Sheffield United defender pushing the Everton striker to the ground, but the initial decision of a yellow card stood, with the Blades keeping all 11 men on the field.
Everton keep another clean sheet
Everton goalkeeper Jordan Pickford had to be alert to keep out a powerful drive from Andre Brooks late in the first period, and the half-time whistle blew with the Toffees, who had five shots on target in the opening 45 minutes, leading courtesy of Doucoure's header.
Ben Brereton Diaz just missed the target with a powerful drive in the 57th minute, before the on-loan Blades forward headed narrowly over the crossbar 10 minutes later.
Archer also came close for Sheffield United late on, with Chris Wilder's side pushing for the leveller in the second period, but Everton managed to post yet another clean sheet.
Jarrad Branthwaite was again outstanding in the middle of the Everton defence, and it will be fascinating to see what happens with the Englishman during this summer's transfer window.
Amadou Onana and Calvert-Lewin are also among those likely to be the subject of interest, with Everton's off-the-field issues potentially leading to some key players leaving in the upcoming market.