1.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):

1830

Sampson, David

PA

Washington Co.

East Finly Twp

p. 328

There is only one David SAMPSON in the county, and he has to be David Sr. (David Jr. has not yet married, so wouldn't be expected to appear in the census).

2.  Census Index:  U.S. Selected Counties, 1840 (Broderbund CD-316):

1840

Sampson, David

PA

Washington Co.

E Findley Twp

p. 173

There is only one David SAMPSON in county.  David Jr. is now married with children, so we would expect him to appear in the census.  If David Sr. is still alive, he is presumably living with David Jr. or one of his other sons.  The numerical data should answer if and which.

3.  1850 Census Index/Images (online at Ancestry.com; Image #10 of 31):  West Finley Twp., Washington Co., PA, p. 541B, 78/78, enumerated 25 Oct 1850 (extracted by Diana Gale Matthiesen):

David Sampson	89	M	none		Md
David     "	42	M	Farmer	1400	"
Fanny     "	35	F			Pa
Mary A    "	13	F			"
Catharine "	12	M			"
Nanacy    "	9	F			"
Henry     "	7	M			"
John      "	2	M			"

4.  Email from Bob Martin.