u/YourMcCoy

Strictly speaking about fugues written for a single instrument, I believe there's only a few five-voice fugues:

• BWV 849 Prelude and Fugue in C-sharp Minor from the WTC 1 No. 4
• BWV 867 Prelude and Fugue in B-flat Minor from WTC1 No. 22
• BWV 534 Prelude and Fugue in F Minor
• BWV 552 Prelude and Fugue in E-flat Major
• BWV 547 Prelude and Fugue in C Major (which I've only heard of recently, it has a last-minute fifth entry towards the end).

And then of course for six-voice fugues, the formidable Ricercar a 6 (BWV 1079).

I'd love to hear if there's any others that may be hidden in ensemble works like what seems to be a five-voice fugue in Kyrie eleison (see 2:22 in the video) at the start of the Mass in B Minor (BWV 232).