Agnes may be "Daughter D."
As the last unmarried daughter, Mary may be fibbing about her age.
The following is said to be our subjects' child, but without knowing his birthdate, I don't know where to place him in the above sequence.
.  David STREET

1.  Jordan R. Dodd, ed.  1993.  Virginia Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):

Street, John

Mims, Agnes

Jan 3, 1801

Goochland Co.

2a.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313).  Please see my WARNING regarding use of this database (the numerical data have the genders switched).  In this particular case, the gender switch doesn't matter, but I like to alert users to this problem whenever I can.  This record is also missing the slave holdings, which seems to be the case for all of the KY and VA records on the CD. 

1810

Street, John

VA

Goochland Co.

p. 435

20010-2001000

2b.  1810 Census Images (online at Ancestry.com; Image #35 of 44; extracted by Diana Gale Matthiesen):

1810

VA

Goochland Co.

p. 435B

John Street

20010-20010-02

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	9 or under	1800-1810	= Son B = Son A (b. 1801)
1 male	26-44	1765-1784	= John
2 females	9 or under	1800-1810	= Daughter B = Daughter A
1 female	26-44	1765-1784	= Agnes (b. 1781/2)
2 slaves	all ages	in or bef. 1810	= ? ?

3.  Family Quest Archives:  Kentucky Federal Census 1820: Livingston, Logan, Mason, Mercer, and Todd Counties.  Heritage Quest CD M33-26 (extracted by Diana Gale Matthiesen):

1820

KY

Todd Co.

p. 133

Jno Street

310101-21010-0-200-0100-1001

These data indicate:

No., Race, Gender	Age Class	Therefore Born	Individuals Inferred
3 white males	9 or under	1810-1820	= Gideon (b. 1814/5) = Son C = John H. (b. 1811/2)
1 white male	10-15	1804-1810	= Son B
1 white male	19-25*	1794-1801	= Son A (b. 1801)
1 white male	45 or over	in or bef. 1775	= John
2 white females	9 or under	1810-1820	= Daughter D = Daughter C
1 white female	10-15	1804-1810	= Daughter B
1 white female	26-44	1775-1794	= Agnes (b. 1781/2)
2	people in agriculture
1 male slave	14-25	1794-1806	= ?
1 female slave	13 and under	1806-1820	= ?
1 female slave	45 or over	in or bef. 1775	= ?
*In the 1820 Census, the third column is age class 16-18 and the fourth column is age class 16-25; therefore, any individual in column three is duplicated in column four.  By subtracting the number in column three from the number in column four, you can create an age class "19-25."

4.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):  John not found in Todd Co., KY, and presumably deceased.

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

1840	Street, Agness	KY	Todd Co.	Todd City	p. 269
1840	Street, G.D.	KY	Todd Co.	Trenton	p. 282
1840	Street, John H.	KY	Christian Co.		p. 215

6a.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  District No. 1, Todd Co., KY, p. 232AB, 531/536, enumerated 23/4 Aug 1850 (extracted by Diana Gale Matthiesen):

Geo. R. Rutherford	31	M	Tailor	500	Scotland
Agnes	29	F			Ky
George	6	M			"
James	2	M			"
[next page]
Agnes Street	70	F			Va
Mary	20	F			Ky

6b.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):
(1)  District No. 2, Christian Co., KY, p. 380A, 302/326, enumerated 3 Sep 1850 (full record not extracted):  John H. Street (38, b. VA) and family (wife Susan and seven children).
(2)  Campbellsville, Taylor Co., KY, p. 193B, 626/627, enumerated 17 Sep 1850 (full record not extracted):  G.D. Street (æ 35, b. KY) and family (wife Martha A. and four children).

7a.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1810-1813.   (Self-published; available from author at 4396 Coopertown Rd., Russellville, KY 42276, or from the Christian County Genealogical Society, Hopkinsville, KY):  not found.

7b.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1814-1818.   (Self-published.  This book is out of print.  I do not have a copy.  If you have one to sell, please contact me.)

7c.  A.B. Willhite.   [n.d.]  Christian Co., Kentucky, Tax List, 1819-1823.   (Self-published; available from author at 4396 Coopertown Rd., Russellville, KY 42276, or from the Christian County Genealogical Society, Hopkinsville, KY).

Pg. in Willhite	Year	First Name	Last  Name	A	B	C	D	Acres	Watercourse
62	1819	John	Sheet	1
	1820-23	[not found]
Legend for numerical data: A = White Males 21 or over; B = Blacks over 16; C = Total Blacks; D = Horses

"Sh" is a common mis-reading of "Str."  As expected, John drops off the Christian Co. tax rolls when Todd Co. is formed in 1820.  John's holdings on the tax roll do not approach his known wealth, but for a variety of reasons, people are sometimes exempted from their taxes.  In this case, it may be that John moved into the county just at tax time and the lister gave him a break for that reason.

8.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).

9.  Messages posted to the Mims Family Genealogy Forum (online at GenForum.com).

10.  Messages posted to the MIMMS Surname Board (online at RootsWeb.com/Ancestry.com).

11.  Brandi A. Mims.  Descendants of Thomas Mims. FamilyTreeMaker User Home Page.

12.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).