A bit of confusion with this man could be two Police Kennedy's in Liverpool.
Attested 17 Jan 1878 age 20 B/c 1858 New Inn Clonmel, Cty Tipperary. To 2/18 No.1565, to 1/24 16 Feb 1879 No.2145 [reinforcements] to S Africa 1 March 1879 to 2 Oct 1879. Discharged 14 Jan 1890 12 yrs. Following day enlisted short service reserve 15 Jan 1890 to 14 Jan 1894.
1891 census 25 Jefferson Street, Everton, West Derby, Liverpool, He is a Police Officer B.1859 Ireland, M to Bridget [B.1869 Liverpool] 3 Children.
1901 census 21 Exley Street, West Derby, Liverpool, He Police Sgt B.1858 Dumfrieshire Scotland, M to Annie 5 Children.
1911 census 24A Olive Street Police Station, Liverpool, He Police Sgt B.1858 Dumfrieshire, M.Annie [B.1862 Barmouth Wales].
He probably dies Sept Qtr 1937 in Liverpool North District.
Just to confuse you all i also found another William Kennedy B.1859 Dumfrieshire Scotland attested 21 feb 1877 to 62nd Regt District transferred Military Foot Police 18 Dec 1888, discharged 3 Sept 1889. Neither Military Records mention wife or children, Military Service of Kennedy born Dumfrieshire only service abroad is in Malta.