Protestant records of all sorts would be held by the Church of Ireland, CofI was the dominant church at that time, due to the British takeover. There are few records in Ireland
for census, although they were 1841+ but all but a few
were burned in the Four Courts Fire 1922.

Two forms of census substitutes exist:
1820-30's Tithe(Tax) Applotments (look for William here)
Available, National Archives, Dublin and on Ancestry.com

1853 Griffith Valuation of Kildare There is NO William listed but 26 other MacDonald's in 14 Kildare parish's.

The names of some of the occupants are fairly unusual for the time and if they show up in your John's family you could probably be sure which are brothers, cousins, uncles!

John 3 x, Archibald, Felix, Daniel, Patrick 6, Michael, Geoffrey, Judith, Charles, Francis, Catherine. The women likely widowed as land was generally in men's names but often then the widow would apply to have the land lease in her name.

They didn't own the land but were tenants.
There were the people who owned the land, aristocracy, head-tenants people who would rent large tracts including
ministers who would then sub-let to the sub-tenant or occupier.

eg: the Duke of Leinster

There is an Irish History Foundation that has baptism records for parish's in Kildare, a few going back into the 1700's. 22 RC Parish's and 20 Church of Ireland Parish's.
You would just have to try your luck. The History Foundation is a not for profit but fee paying like most of Ireland's genealogy.

There are directories 1824, 1846 on www.failteromhat.com
and free Griffiths and also directories 1870, 1881, 1894 but
if farmers they do not appears till the last two mentioned.

Any questions: codeannette@yahoo.ca

Annette Code