— born in Washington, DC:
3.  John Lewis STRAUB, b. 1833/4 
4.  Mary Margaret STRAUB, b. 1835/6
5.  Frances STRAUB, b. 1839/40
6.  (John) Joseph STRAUB, b. 1841/2
7.  Robert STRAUB, b. 1845/6; d.s.p. by 1860
8.  Rudolph/Rudolphus Alexander STRAUB, b. 1847/8/9 
9.  Mathias/Matthias STRAUB, b. 1851/2

1.  Marriage Record:

2.  1840 Census Index/Images (online at Ancestry.com):  can't find, at least not in DC, but there are only 4506 entries in the index for DC, so surely the index is not complete.  There were 6529 entries in 1830 and over 20,000 entries in 1850 for DC.

3.  1850 Census Index/Images (online at Ancestry.com; Image #123 of 135):  City of Washington (Ward 3), District of Columbia, Roll 56 (Book 1), p. 205A, 887/887, enumerated 1 Aug 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):¤•

J Straub	50	M		Potter		Germany
Frances "	42	F				ditto
Catharine "	22	F				ditto
Frank     "	19	M		none		ditto
Lewis     "	16	M		ditto		D C
Mary      "	14	F				ditto
Frances   "	10	F				ditto
John      "	8	M				ditto
Robert    "	4	M				ditto
Alexander "	1	M				ditto

4.  1860 Census Index/Images (online at Genealogy.com, Image #146-147 of 236):  Washington (Ward 3), DC, Roll 102 (Book 1), pp. 800-801, PN 146-147, 934/981, enumerated 17/18 Jul 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):¤•

Jos Strawb	60	M		Mass Potter	5000	300	Baden Germany
[next page]
Frances Strawb	50	F					Baden Germany
Francis    "	30	M		Potter			"      "
Margaret   "	21	F					Wash City
Frances    "	19	F					"
Jos        "	18	M		Ap. Tinner			"
Rudolphus  "	12	M					"
Mathias    "	8	M					"

5.  1870 Census Index/Images (online at Genealogy.com, Image #62 of 317):  Washington P.O., Washington, Washington Co., DC, Roll 124 (Book 1), p. 534B, PN 180, 1213/1452, enumerated 11 Jul 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Straub Frances	62	F	W	Keeping House	15000	1000	Baden
______ Frank	40	M	W	Florist			"
______ Joseph	28	M	W				D C
______ Rudolphus	22	M	W	Plasterer			"
______ Frances	26	F	W				"
______ Mathias	17	M	W				"

Francis/Frank appears to have been enumerated twice:  once here, on 11 Jul 1870, before he married, and once again on 8 Aug 1870, after he married.  Joseph is the florist, not Frank, who is a potter.  Daughter Frances is fibbing about her age.

6.  1880 Census (indexed at FamilySearch.org; page image online at Ancestry.com, Image #30 of 55):  636 C Street NW, Washington City, District of Columbia, Roll 122, p. 417A, PN 29, SD 17, ED 41, enumerated 11 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):¤•

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

8

9

11

13

24

25

26

231

299

Straub Frances

W

F

72

/

Keeps House

Baden

Baden

Baden

______ Matthias

W

M

25

Son

/

Potter

DC

Baden

Baden

______ Frances

W

F

36

Dau

/

Gov. Print. Office

DC

Baden

Baden

______ Louis E

W

M

22

Grd Son

/

Brick Mason

DC

DC

Va

______ Theresa

W

F

21

Gd Dau

/

At home

DC

DC

Va

Louis and Theresa are the children of Frances's son, John Lewis STRAUB — I guess they don't like their step-mother.