One secondary source (Hostetler, 1970; see below) shows Elmer's wife as "Maggie" STROUP, b. 18 Oct 1882, daughter of these parents:
Father:  Levi B. STROUP
Mother:  Magdalena HOSTETLER
The evidence I have so far gathered shows these two "Maggie's" to be different women.  If you have evidence to the contrary, please share.

1.  LDS.  Family Search: Internet Genealogy Service:  IGI - International Genealogical Index (online at FamilySearch.org).

Elmer C. SWEIGARD Father: M. William; Mother: Rebecca Marriage: 18 Dec 1902, Penbrook, Dauphin, Pennsylvania Spouse: Margaret L. STROUP Mother: Margaret Source: "Extracted marriage record for locality listed in the record."

2.  1880 Census Every-Name-Index/Images (online at Ancestry.com):  William SWIGARD (æ 21, b. PA) is living in Halifax Twp., Dauphin Co., PA (p. 73D), with his wife, Rebecca (æ 20, b. PA).

3.  1890 Census:  the 1890 Census Population Schedules were destroyed.

4a.  1900 Census Every-Name-Index/Images (online at Ancestry.com):  Elmer C. SWIEGERT (b. Mch 1883, PA) is living in Susquehanna Twp., Dauphin Co., PA (p. 299A), with his parents, M.W. SWIEGERT (b. Aug 1859, PA) and Rebecca (b. Nov 1864, PA).

4b.  1900 Census Every-Name-Index/Images (online at Ancestry.com, Image #5 of 27):  Susquehanna Twp. (Southern Pct.), Dauphin Co., PA, Roll T623_1403 (Book 1), p. 278A, SN 12, SD 9, ED 93, enumerated 14 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):¤•

1900:  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	7	8	9	10	11	12	13	14	15	19	20	22	23	24	25	27	28
237	341	Haverstick Edward	Head	W	M	Mar 1874	26	M	3			PA	PA	PA	Farmer	0	Y	Y	Y	R	F	25
		[Edward's wife and children, et al.]
		Stroup Foster	Boarder	W	M	Dec 1882	17	S				PA	PA	PA	Farm laborer	0	Y	Y	Y
		Stroup Maggie	Servant	W	F	Oct 1884	15	S				PA	PA	PA	Servant	0	Y	Y	Y

Foster STROUP is presumed to be Maggie's brother.

5.  1910 Census Index/Images (online at Ancestry.com, Image #56 of 65):  Susquehanna Twp., Dauphin Co., PA, Roll T624_1337 (Part 2), p. 265A, SN 33A, SD 14, ED 113, enumerated 6 May 1910, official enumeration date 15 Apr 1910 (extracted by Diana Gale Matthiesen):¤•

1910:  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	7	8	9	10	11	12	13	14	17	18	19	20	21	22	23	24	25	26	28	29
538	540	Sweigard Elmer C	Head	M	W	27	M1	8			PA	PA	PA	Eng	Farmer	Home farm	Emp			Y	Y		R	F	16
		________ Margaret L	Wife	F	W	26	M1	8	2	2	PA	PA	PA	Eng	Farm laborer	Home farm	W	N	0	Y	Y
		________ Melvin L	Son	M	W	6	S				PA	PA	PA		None							Y
		________ Margaret E	Dau	F	W	1 8/12	S				PA	PA	PA		None

6.  1920 Census Every-Name-Index/Images (online at Ancestry.com, Image #19 of 31):  614 Woodbine St., Harrisburg City (Ward 10), [Susquehanna Twp.,] Dauphin Co., PA, Roll T625_1559 (Book 1), p. 92A, SN 10A, SD 12, ED 99, enumerated 8 Jan 1920, official enumeration date 1 Jan 1920 (extracted by Diana Gale Matthiesen):¤•

1920:  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

7

8

9

10

11

12

16

17

18

19

21

23

25

26

27

28

*

614

207

223

Sweigard Elmer C

Head

O

F

M

W

39

W

Y

Y

PA

PA

PA

Y

car-repairman

steam-railroad

W

________ Melvin L

Son

M

W

16

S

Y

Y

Y

PA

PA

PA

Y

None

________ Margaret E

Dau

F

W

11

S

Y

Y

Y

PA

PA

PA

Y

None

Bower Maud I

housekeeper

F

W

31

S

Y

Y

PA

PA

PA

Y

housekeeper

*Woodbine St

7.  1930 Census Every-Name-Index/Images (online at Ancestry.com, Image #9 of 13):  134 Curtin Street, Penbrook Borough (Ward 1), Dauphin Co., PA, Roll 2028 (Book 1), p. 84A, SN 5A, ED 22-87, SD 19, enumerated 8 Apr 1930, official enumeration date 1 Apr 1930 (extracted by Diana Gale Matthiesen):¤•

1930:  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

7

8

9

10

11

12

13

14

15

16

17

18

19

20

24

25

26

27

28

29

30

*

124

105

111

Sweigard Elmer

Head

O

7,000

R

N

M

W

47

M

??

N

Y

PA

PA

PA

Y

Inspector

Rail Road

W

Y

N

________ Maud

Wife

F

W

42

M

33

N

Y

PA

PA

PA

Y

None

________ Elmer

Gran-Son

M

W

5

S

N

PA

PA

PA

None

________ Margaret

Dau

F

W

21

S

N

Y

PA

PA

PA

Y

Helper

Typewriter Works

W

N

19

*Curtin Street

For Elmer to be their grandson, he has to be the son of Elmer's only son, Melvin L. SWEIGARD.  Listed next to our subject's widowed mother, Rebecca SWEIGARD (æ 67, b. PA).

8.  Harvey Hostetler.  1912 [reprinted 1970].  Descendants of Jacob Hochstetler.  Gospel Book Store, Berlin, OH 44610 [excerpt courtesy of Sue Davis].  On p. 713:

6607, Magdalena Hostetler, 6606, Sapulpa, Okl., was b. July 4, 1848, and m. Levi Stroup who d. in 1891.  [children] David H., 6608; Sallie H., 6609; William H., 6611; John H., 6612; Andrew H., ; Lee R., July 28, 1882 - ; Maggie, 6613.

6613, Maggie Stroup, 6607, Linglestown, Pa., R. 2, was b. Oct. 18, 1882, and m. Dec. 18, 1902, Elmer Clayton Sweigard, son of Michael William and Rebecca (Radel) Sweigard, Linglestown, Pa.  United Brethren church.  Melvin Leroy, July 28, 1908.

This book is the apparent source of the error mis-identifying Margaret L. STROUP (b. Oct 1884) as "Maggie" (b. Oct 1882), daughter of Levi & Magdalena (HOSTETLER) STROUP.  My research shows these are two different women.  Also, based on the 1910 census, it was Margaret, not Melvin Leroy, who was born in Jul 1908.