Middle initial from pension application record (could be a C). But reocord shows
Civil War Pension Index: General Index to Pension Files, 1861-1934 about Isaac H. Coates
C 55 Mass Inf
Name: Isaac H. Coates
State Filed: Missouri - not Maryland!
Widow: Mary B. Coates10
Could be t was misread, but looks like Mo., not Md.

Tombstone in John Wesley Church Cemetery, Libertytown, MD
Isaac Coates
Co. 1 55 MASS INF
May 20, 1906
Aged 62 Years
photograph P8307211 copy.JPG, P830721.JPG

1900 Census, Mt Pleasant, Fred Co, MD #274
William H Coates 23, Jan 1877, 23, M2, MD,MD,MD, farmer
Fannie A Coates , wife, 30, Jan 1870, M2, children 0,0, MD,MD,MD
Isaac Coates , father, 55, Aug 1844, Wd, , MD,MD,MD, farm laborer
Cordelia Thomas 69, mother-in-law, wd, MD,MD,MD

1880 Census, Mt. Pleasant, Fred. Co., MD, #209
all MD,MD,MD
Isaac Coats 38, laborer
Mary Coats 29
Charles Coats 13
Elizabeth Coats 11
William Coats 4

1870 Census, Liberty Dist, Fred. Co, #
Loyd Griffeth (W) 47
Lousia Griffeth (W) 43
Thomas H Griffeth (W) 15
Rasin H Griffeth (W) 12
Mollie Griffeth (W) 18
Lyd N Griffeth (W) 10
Henry R B Griffeth (W) 7
Verginia R Griffeth (W) 6
John C Griffeth (W) 2
Isaac Coats 27, works on farm
Mary Coats 20
Charles Coats 3
Elizebeth Coats 1

Not found in 1860 or 1850 census
------------
1850 Slave Census
40 Female Black Delitha Coates Bladensburg, Prince George's, Maryland
13 Male Black Delitha Coates Bladensburg, Prince George's, Maryland
8 Male Black Delitha Coates Bladensburg, Prince George's, Maryland
[remote possibility this could be Isaac]

1850 Census, Bladensburg, Prince Georges Co, Md #139
Deletha Coates (W) 18, farmer, MD
--------------
Deletha not found in
In PG County Slave Statistics Commissioner Report
40230-6-3 Burroughs, Richard D. 4 13 Jun 1867 Coats, Eliza 35 F Good Life
40230-6-3 Burroughs, Richard D. 4 13 Jun 1867 Coats, Maria 16 F Good Life
40230-6-3 Burroughs, Richard D. 4 13 Jun 1867 Coats, Isaac 14 M Good Life
40230-6-3 Burroughs, Richard D. 4 13 Jun 1867 Coats, Phyllis 12 F Good Life
40230-6-3 Burroughs, Richard D. 4 13 Jun 1867 Coats, Jim 10 M Good Life

Other Coates families:

40230-32 Duvall, Dr. William W. 1 29 Nov 1867 Coates, Aurelia 67 F Good Life
40230-32 Duvall, Dr. William W. 1 29 Nov 1867 Coates, Mark 28 M Good Life

40230-42 Hill, Philip 2 27 May 1867 Coates, Maria 36 F Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Priscilla 14 F Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Patrick 12 M Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Julius 10 M Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Henry 8 M Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, George 4 M Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Kitty 18 F Good Life
40230-42 Hill, Philip 2 27 May 1867 Coates, Henry 2 M Good Life

40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Anthony 18 M Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Emily 42 F Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Beall, Sarah 25 F Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Sarah 16 F Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Columbus 11 M Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Henderson, John 8 M Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Lucretia 14 F Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Rosa 12 F Good Life
40230-5 Bowie, John W. 3 6 Jun 1867 Coates, Josephine 7 F Good Life