County secondary schools in Kenya form the third tier after national and extra-county schools respectively.
Most of Kenyan learners are absorbed by these schools.
Admission to county schools is done online by the Ministry of Education.
They are either mixed or single-sex.
Here is a list of county secondary schools in Tharaka Nithi County:
| NAME | KNEC CODE | TYPE | CATEGORY | |
| 1 | KAMBANDI SECONDARY SCHOOL | 19308303 | Mixed | County |
| 2 | KIREGE SECONDARY SCHOOL | 19308305 | Mixed | County |
| 3 | KIERENI SECONDARY SCHOOL | 19308307 | Mixed | County |
| 4 | KIUNGUNI DAY SECONDARY SCHOOL | 19308315 | Mixed | County |
| 5 | RUBATE SECONDARY SCHOOL | 19308506 | Mixed | County |
| 6 | MPUKONI SECONDARY SCHOOL | 19308507 | Mixed | County |
| 7 | NDAGONI GIRLS SECONDARY SCHOOL | 19308509 | Girls | County |
| 8 | KIAMURIUKI SECONDARY SCHOOL | 19308510 | Mixed | County |
| 9 | MAGENKA SECONDARY SCHOOL | 19308512 | Mixed | County |
| 10 | GATUNGA SECONDARY SCHOOL | 19313102 | Boys | County |
| 11 | MARIMANTI GIRLS HIGH SCHOOL | 19313104 | Girls | County |
| 12 | CHIAKARIGA GIRLS SECONDARY SCHOOL | 19313204 | Girls | County |
| 13 | CHIAKARIGA SECONDARY SCHOOL | 19313206 | Mixed | County |
| 14 | P.C.E.A MURAGA SECONDARY SCHOOL | 19326106 | Mixed | County |
| 15 | ST. AUGUSTINE RUGUTA SECONDARY SCHOOL | 19326107 | Mixed | County |
| 16 | MUGONA GIRLS SECONDARY SCHOOL | 19326108 | Girls | County |
| 17 | ACK IGANGARA SECONDARY SCHOOL | 19326110 | Mixed | County |
| 18 | ITARA DAY SECONDARY SCHOOL | 19326112 | Mixed | County |
| 19 | THIGAA SECONDARY SCHOOL | 19326205 | Mixed | County |
| 20 | NGERU SECONDARY SCHOOL | 19326209 | Boys | County |
| 21 | NTURIRI BOYS` SECONDARY SCHOOL | 19326210 | Boys | County |
| 22 | KIEGANGURU GIRLS SECONDARY SCHOOL | 19326215 | Girls | County |
| 23 | ST ANN GIRLS SECONDARY SCHOOL | 19326216 | Girls | County |
| 24 | MUKOTHIMA GIRLS’ SECONDARY SCHOOL | 19342102 | Girls | County |
| 25 | NTUMBARA SECONDARY SCHOOL | 19367401 | Mixed | County |
| 26 | KAJIAMPAU MIXED SECONDARY SCHOOL | 19367404 | Mixed | County |
| 27 | KAJUKI SECONDARY SCHOOL | 19367406 | Mixed | County |
| 28 | ITUGURURU SECONDARY SCHOOL | 19367501 | Mixed | County |
| 29 | M.C.K KIANGIRI SECONDARY SCHOOL | 19367502 | Mixed | County |
| 30 | KAMWIMBI SECONDARY SCHOOL | 19367504 | Mixed | County |