Colchester sealed their automatic promotion to the Championship with a nervy draw at Huish Park.
Yeovil's Paul Terry challenges Colchester's Neil Danns
United only needed to avoid defeat to go up and had chances to win it through Neil Danns' close-range header and Greg Halford's parried shot.
Yeovil almost provided a shock when David Poole shot wide when clean through on goal and Phil Jevons tested Dean Gerken with a low-left foot drive.
But the U's hung on for a draw that put them up at the expense of Brentford.
United were always favourite to claim second spot with Brentford needing to win at Dean Court and the U's needing to lose at Yeovil.
And the visitors started brightly with Scott Vernon heading wide from a long throw.
At the other end the lively strike pairing of Jevons and Arron Davies brought good saves from Gerken.
Colchester went close in the second half when Halford found the on-rushing Chris Iwelumo with a low cross, but the striker shot narrowly wide.
Kevin Watson had a penalty appeal turned down for the visitors, but it was the home side that dominated.
Brentford's draw at Dean Court was not enough for the Bees so Colchester will be playing in the second tier of English football for the first time in their history.
Yeovil: Collis, Lindegaard, Lockwood, Skiverton, Miles, Poole (Harrold 75), Terry, Rocastle, Cohen, Jevons, Davies (Williams 86).
Subs Not Used: Gall, Amankwaah, Guyett.
Colchester: Gerken, White, Chilvers, Vernon (Thorpe 81), Duguid, Halford, Danns, Watson, Baldwin, Iwelumo, Campbell-Ryce (Izzet 76).
Subs Not Used: Cousins, Richards, Clarke.
Colchester are promoted
Ref: A Marriner (W Midlands).