Chelsea will now face a London derby against Arsenal in the final at Selhurst Park on March 5 as they seek their third League Cup title in four years after falling to Manchester City in the final a year ago.
After a scoreless 90 minutes in the first semifinal Wednesday between Arsenal and Manchester City, Chelsea wasted little time in Dagenham, breaking the deadlock just 200 seconds in when Kerr volleyed in Guro Reiten's dinked free kick.
Blues' fans didn't have long to wait for the second with Kerr involved again, this time setting up Fran Kirby who sliced through the Hammers' high defensive line before letting fly to the bottom left corner.
Kerr added the third 10 minutes later, once again benefiting from Reiten's delivery to curl the ball into Mackenzie Arnold's top right corner.
In control of the game, Chelsea were dealt a blow when Kirby had to leave the pitch before half-time having received two minutes of medical attention for a complaint with her knee.
Despite that blow, the visitors continued to show their ruthlessness. Kerr rounded out her hat trick in first-half stoppage time when she raced onto a mishit pass from West Ham defender Hawa Cissoko to fire home.
With little to lose, Hammers' boss Paul Konchesky opted for a quadruple sub at half-time, including bringing on Lucy Parker who was still having her minutes managed after a lengthy injury layoff. But things went from bad to worse for the hosts when Parker was forced off before the hour.
The injury to the English defender was sandwiched between another pair of Chelsea goals, firstly a flowing team move that was capped off with a flourish by Lauren James before Kerr nabbed her fourth of the night with a leaping header.
Involved throughout, Reiten made it seven on 65 minutes when her low effort took a sizable deflection off Hammers defender Grace Fisk to wrong-foot Arnold as it rolled just inside of the left post.
With 25 minutes still left on the clock, the visitors could have scored more but began to ease off with seven goals more than enough to seal another final spot.