| Regimental number | 589 |
| Place of birth | Brisbane, Queensland |
| School | Public School |
| Religion | Church of England |
| Occupation | Railway employee |
| Address | Chinchilla, Queensland |
| Marital status | Single |
| Age at embarkation | 22 |
| Next of kin | Sister, Miss Ruby Kostin, c/o W J Farr, Cnr Montigue Road and Raven Street, Hill End, South Brisbane, Queensland |
| Enlistment date | |
| Rank on enlistment | Private |
| Unit name | 42nd Battalion, C Company |
| AWM Embarkation Roll number | 23/59/1 |
| Embarkation details | Unit embarked from Sydney, New South Wales, on board HMAT A30 Borda on |
| Rank from Nominal Roll | Private |
| Unit from Nominal Roll | 41st Battalion |
| Other details from Roll of Honour Circular | Died of Pneumonia |
| Fate | Died of disease |
| Place of death or wounding | Abbeville, France |
| Age at death | 25 |
| Age at death from cemetery records | 25 |
| Place of burial | Abbeville Communal Cemetery Extension (Plot V, Row E, Grave No. 32), France |
| Panel number, Roll of Honour, Australian War Memorial | 134 |
| Miscellaneous information from cemetery records | Parents; Frederick John and Jane KOSTIN |
| Family/military connections | Cousin: Pte Reg Farr who was killed in action on the Somme on 7th June, 1917. - Same day as William Kostin was wounded. |