Langer, playing in his last county championship match before returning home, led Somerset to 442 for two in their first innings against Surrey.
He finished the day on 234 not out from 279 balls with 31 fours and two sixes.
It was also the highest ever individual score at Guildford, beating the previous best of 228 recorded by Darren Bicknell in 1995.
Langer overshadowed Indian spinner Anil Kumble who was playing his first match for Surrey. By the close, Kumble had conceded 100 runs from 28 overs.
In Division One, leaders Sussex built up a commanding total against bottom side Middlesex thanks to an unbeaten century by Chris Adams at Southgate.
Adams was unbeaten on 101 and Luke Wright was 41 not out as the visitors ended the day on 374 for five.
Lancashire were in danger of succumbing to a crushing defeat despite the presence of England all-rounder Andrew Flintoff against Kent at Canterbury.
Matt Walker made 197 after putting on 121 with tailender Amjad Khan as the hosts finished on 440 all out.
Lancashire then lost two quick wickets in reply as Mark Chilton (one) and Iain Sutcliffe (six) both fell for just 12 runs.
Mal Loye steadied the Red Rose county's nerves with an unbeaten 38 and will resume with Stuart Law who made 11 as Lancashire finished on 56 for two, still 166 runs adrift.
Australian paceman Jason Gillespie took four wickets and Tim Bresnan claimed three as Yorkshire reduced Warwickshire to 201 at Scarborough.
Only Heath Streak (68 not out), Ian Westwood (31) and Paul Harris (32) made significant contributions although it could have been far worse as the visitors were 122 for nine at one point before Streak and Harris put on 79.