Douglass, Dowglas, and Douglas, in c1630 Ulster Muster rolls 
http://www.therjhuntercollection.com/resources/muster-rolls-c-1630/search-muster-rolls/

First Name	Surname	Barony/Lands	Landlord/Estate	County
Robert	Douglass	Glennarme	Earl of Antrim's British tenants	Antrim
John	Douglass		Lord Viscount Ards	Down
William	Douglass		Lord Viscount Ards	Down
James	Douglass		Lord Viscount Ards	Down

First Name	Surname	Barony/Lands	Landlord/Estate	County
William	Dowglas	Fewes	Lord Mountnorrice	Armagh

First Name	Surname	Barony/Lands	Landlord/Estate	County
John	Douglas	Loughty	Mr Moynes	Cavan
John	Douglas	Clougher	Sir J. Erskin	Tyrone
George	Douglas	Dungannon	Captain A. Sanderson	Tyrone
John	Douglas	Dungannon	Captain A. Sanderson	Tyrone
Archbald	Douglas	Omy	Sir P. Crosby	Tyrone
John	Douglas	Strabane	Strabane Town	Tyrone
Gawen	Douglas	Dungannon	Lord Primate of Armagh	Tyrone
Richard	Douglas	Dungannon	Lord Primate of Armagh	Tyrone
Robert	Douglas	City and Liberties	Londonderry (including Goldsmiths' estate)	Londonderry
Alexander	Douglas	City and Liberties	Londonderry (including Goldsmiths' estate)	Londonderry
John	Douglas	City and Liberties	Londonderry (including Goldsmiths' estate)	Londonderry
George	Douglas	City and Liberties	Londonderry (including Goldsmiths' estate)	Londonderry
John	Douglas		Sir R. Macclelan (Haberdashers)	Londonderry
George	Douglas	Dunluce	Earl of Antrim's British tenants	Antrim
David	Douglas	Glennarme	Earl of Antrim's British tenants	Antrim
George	Douglas	Belfast	Mr Edmonston	Antrim
William	Douglas	Rapho	Duke of Lynox	Donegal
John	Douglas	Rapho	Duke of Lynox	Donegal
Hector	Douglas	Boylagh and Bannagh	Earl of Annandall	Donegal
William	Douglas	Boylagh and Bannagh	Earl of Annandall	Donegal
William	Douglas	Eneshone	Lord Chichester	Donegal
William	Douglas		Lord Viscount Ards	Down
Thomas	Douglas	great Ardes	Lord Viscount Clannaboyes	Down
William	Douglas	town of Dunmoore [Dromore] and Lower Euvagh	Bishop of Dromore	Down
James	Douglas	town of Dunmoore [Dromore] and Lower Euvagh	Bishop of Dromore	Down
John	Douglas	town of Dunmoore [Dromore] and Lower Euvagh	Bishop of Dromore	Down