Can’t identify him in the 1911 census: have been through all 48 entries for an 1898 birth plus or minus one year.  And no results for plus or minus 5 years and with India in the entry (for his birth).

But his baptism is clearly identifiable, in India:

First name(s) Charles Ian Hamilton
Last name Hill
Birth year 1898
Birth date 23 Jul 1898
Baptism year 1898
Baptism date 23 Jul 1898
Place Chudderghaut
Presidency Madras
Father's first name(s) Claude Hamilton Archer
Father's last name Hill
Mother's first name(s) Frances Mary
Archive reference N-2-84
Folio 10
Catalogue descriptions Parish register transcripts from the Presidency of Madras
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In London Gazette of 5 June 1917, p. 5693, he was commissioned at 2 Lt wef 13 May 1917,
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TNA Has record for his Military Service at WO 339/84819: “2/Lieutenant Charles Ian Hamilton HILL  The Royal Welsh Fusiliers.”  The date is “[1914-1922]”
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In 1939 he was a stockbroker, though at a mental hospital:

P Cassel Hospital, Swaylands Penshurst , Sevenoaks R.D., Kent, England

FIRST NAME(S) LAST NAME(S) ROLE DOB SEX OCCUPATION  MARITAL STATUS  SCHEDULE  SCHEDULE SUB NUMBER

Charles Ion Hamilton Hill P 23 Jul 1898 Male Stockbroker  Single  1  18

I wonder if this was a result of some trauma from his WW1 service?
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No marriage can be identified as his.

Possibly his will might show any dependant.
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His death:

First name(s) CHARLES ION H
Last name HILL
Gender Male
Birth day 23
Birth month 7
Birth year 1898
Death quarter 2
Death year 1983
District WESTMINSTER
County London
Volume 15
Page 1800
Country England
Record set England & Wales deaths 1837-2007
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His probate index:

HILL, Charles Ion Hamilton of 15 Welbeck Street, London W1 died 27 June 1983  Probate London 7 September £61162  830014219C
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