1.  Wales, Glamorgan, Parish Register, Marriages, 1837-1922  (online at familysearch.org):

Name	William David	William David
Event Date	26 May 1848	14 Jul 1866
Event Place	Llangynwyd, Glamorgan	Coity, Glamorgan
Marital Status	Single	Widowed
Father	Edward David	Edward David
Spouse	Margaret Thomas	Ann Delahay
Spouse's Marital Status	Single	Single
Spouse's Father	Thomas Thomas	Robert Delahay
Digital Folder | Image	4188875 | 193	4173955 | 146

William may have had a second marriage, and this may be it.  Coity is a village in today's Bridgend County Borough, within about 5 miles of Maesteg.

2.  1841 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com):  can't find with certainty, mainly because birthplace was not recorded beyond Glamorgan.  He may be the William DAVID (æ 15, b. GLA) living with the EVANS family in St. Bride Major, GLA, which is the closest match geographically.

3.  1851 Census of England Every-Name-Index/Images (online at Ancestry.com, Image #49 of 85):  official enumeration date 30 Mar 1851 (extracted by Diana Gale Matthiesen):

Class	GSU Roll	Reg. Dist.	Reg. Sub-dist.	County	ED	Piece	Folio	Pg
HO107	104206-104208	Bridgend	Maesteg	Glamorgan	3c	2461	112	48

Parish or Township of	Eclesiastical District of	City of Borough of	Town of	Village of
Cwmdu				Maesteg

1851:  for an explanation of the column headings, please see What the Numbers in the British Censuses Mean.
1	2	3	4	5	6a	6b	7	8		9
156	Temple St	W Davis	Head	Mar	26		Miner	St Brides	Glamorgan
		Margaret Davis	Wife	Mar		25		Llangynwyd	Do
		Thomas Davis	Son		2			Do	Do
		Mary Thomas	Lodger	Unm		21	Laborer	Do	Do

It's very likely Mary is Margaret's sister.

4.  1861 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com, Image #9 of 22):  official enumeration date 7 Apr 1861 (extracted by Diana Gale Matthiesen):

Class	GSU Roll	Reg. Dist.	Reg. Sub-dist.	County	ED	Piece	Folio	Pg
RG9	543230	Bridgend	Maesteg	Glamorgan	8	4073	58	8

Parish [or Township] of	City or Municipal Borough of	Municipal Ward of	Paliamentary Borough of	Town of	Hamlet or Tything, &c., of	Eclesiastical District of
Llangynwyd				Maesteg	Cwmdu

1861:  for an explanation of the column headings, please see What the Numbers in the British Censuses Mean.

1

2

3a

3b

4

5

6

7a

7b

8

9

10

48

8 Rose Cottages

/

William Davies

Head

Mar

37

Coal Miner

St Brides

Glamorgan

Margaret  do

Wife

Mar

36

Llangynwyd

do

Thomas    do

Son

12

Coal Miner

do

do

Edward    do

"

9

Scholar

do

do

David     do

"

6

do

do

do

William   do

"

2

do

do

5.  1871 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com, Image #35 of 68): official enumeration date 2 Apr 1871 (extracted by Diana Gale Matthiesen):

Class	GSU Roll	Reg. Dist.	Reg. Sub-dist.	County	ED	Piece	Folio	Pg
RG10	848037	Bridgend	Maesteg	Glamorgan	5	5412	81	35

Civil Parish [or Township] of	City or Municipal Borough of	Municipal Ward of	Paliamentar Borough of	Town of	Village or Hamlet, &c., of	Local Board or  Improvement District of	Eclesiastical District of
Llangonoyd*				Maesteg	Cwmdu	Cwmdu

*Llangonoyd is an alternate name or spelling of Llangynwyd, the usual name for this parish.

1871:  for an explanation of the column headings, please see What the Numbers in the British Censuses Mean.

1

2

3a

3b

4

5

6

7a

7b

8

9

10

172

21 Alfred St.

/

William David

Head

Mar

46

Collier

Glam

Ogmore

Ann      Do

Wife

Mar

47

Do

Bridgend

William  Do

Son

12

Scholar

Do

Maesteg

6.  1881 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com, Image #57 of 86, official enumeration date 3 Apr 1881 (extracted by Diana Gale Matthiesen):

Class	GSU Roll	Reg. Dist.	Reg. Sub-dist.	County	ED	Piece	Folio	Pg
RG-11	1342283	Bridgend	Maesteg	Glamorgan	10	5327	63	56

Civil Parish [or Township] of	City or Municipal Borough of	Municipal Ward of	Paliamentary Borough of	Town or Village or Hamlet of	Urban Sanitary District of	Rural Sanitary District of	Eclesiastical Parish or District of
Cwmdu				Maesteg*	Maesteg		Llangynwyd

*Cwmdu was struck out, and Maesteg was entered in another hand.

1881:  for an explanation of the column headings, please see What the Numbers in the British Censuses Mean.

1

2

3a

3b

4

5

6

7a

7b

8

9

10

286

59 Bethania St.

/

William Davies

Head

Mar

56

Collier

Glam

St Bride

Ann       Do

Wife

Mar

57

Do

Bridgend

William   Do

Son

Unm

22

Collier

Do

Maesteg

Is "Ann" Margaret's middle name, or has William remarried?

7.  1891 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com):  Widower William DAVIES (æ 66, b. St. Brides, GLA) is living in Maesteg, GLA, with his married son, David DAVIES, and his family (q.v.).

8.  1901 Census of England and Wales Every-Name-Index/Images (online at Ancestry.com):  can't find.

9.  Public Member Trees (online at Ancestry.com).

10.  WorldConnect / Ancestry World Trees (online at wc.rootsweb.ancestry.com).