Lacoste? Lacoast?

Difficult to answer this enquiry. The name Lacoste (and variants) is not a name commonly found in Ireland, as you have already discovered. Looking at the 1901 Irish census there’s a handful of people with La and Le names but they are nearly all English or French. There are no Lacoste or Lecoste (or similar) deaths in the civil indexes, so there doesn’t appear to have ever been a settled family in Ireland, or at least not one that spelled the name the way you are now familiar with.

If your ancestor came from Co Down then I suspect the name has been changed somewhere over the years. Alternatively perhaps his parents were only in Ireland briefly and normally lived elsewhere. You could try DNA testing to see what that throws up.

www.rootsireland.ie/ has 1 baptism & 4 burials - all from Ballyclutter, Down

Name:Elizabeth LacosteDate of Birth:29-Jun-1862
Date of Baptism:10-Jul-1862Address:Green Row AudleystownParish/District:BALLYCULTERGender:FemaleCountyCo.

Down
Denomination:Church of Ireland
Father:William LacosteMother:Rose AnneOccupation:Boat Man

Name:BLacosteDate of Death:04-Jan-1859
Age:74Parish / District:BALLYCULTERAddress:CastlewardCounty:Co. DownStatus:
Denomination:Church of IrelandOccupation:
Sex:Male

Name:BlaizeLacosteDate of Death:04-Jan-1859
Age:74Parish / District:Ballyculter CIAddress:CastlewardCounty:Co. DownStatus:
Denomination:Church of Ireland

Name:WilliamLacosteDate of Death:16-Oct-1862
Age:39Parish / District:BALLYCULTERAddress:AudleystownCounty:Co. DownStatus:
Denomination:Church of IrelandOccupation:
Sex:Male

Name:WilliamLacosteDate of Death:16-Oct-1862
Age:39Parish / District:Ballyculter CIAddress:The Green Row AudleystownCounty:Co. DownStatus:
Denomination:Church of Ireland

There is also a Lacoast:
Name:AnneLacoastDate of Death:04-Dec-1830
Age:
Parish / District:BALLYCULTERAddress:AudleystownCounty:Co. DownStatus:
Denomination:Church of IrelandOccupation:
Sex:Female

Col

Found a few more Lacoasts:

Church BaptismLacoastMargaret1818Co. Down
Church BaptismLacoastAlexandra1819Co. Down
Church BaptismLacoastWilliam1821Co. Down
Church BaptismLacoastJane1826Co. Down
Church BaptismLacoastAnne1830Co. Down

Parents are Blaze Lacoast & Ann address Audsleytown Ballyclutter C of I Parish

here's parents' marriage:

Date of Marriage:25-Dec-1816
Parish / District:DOWN
County:Co. Down
Husband
WifeName:BLacoast
AnneLeathesAddress:Castleward
CastlewardDenomination:Church of Ireland
Church of IrelandOccupation:SAILOR
Age:
Status:
Husband's Father
Wife's FatherName:
Lacoast
LeathesAddress:

Church:  BALLYCULTER Church of Ireland
REV C WOLSELEY MGR HUSBANDS FIRST NAME ENTERED IN THE REGISTER AS
BLAZE.

Col

I just noticed your reply.  Thank you so much.  I will definitely look at these, they are a lot more than I've found so far!  I'm wondering if he changed his name when he immigrated.  Thank you.