There are 2 types of tenor banjos. 17 fret and 19 fret tenor banjos. Both can be tuned in any of the tunings below.
C, G, D, A
Standard Tenor Tuning
The most standard tenor banjo tuning. This tuning is the intervals of fifths and is exactly the same as viola or mandola.
G, D, A, E
Irish Tenor Tuning
This tuning is also in fifths but is lower in pitch than the standard tenor tuning. This tuning is like a violin or mandolin, only one octave lower.
D, G, B, E
Chicago Tuning
This tuning is the same as the top four strings of a guitar. This makes it very easy for guitarists to pick up a 4-string banjo and start playing.