I believe you're correct about Hannah LEATHERMAN marrying John BAKER, Sr., but I don't have proof, either. There's a RootsWeb message that says they MAY BE parents of John BAKER (18 July 1801 - 11 Sep. 1874, bu. Grossnickle's Brethren Cem., Ellerton, MD).

Margaret E. MYERS' Marriage Licenses of Fredk. Co., MD:

LEATHERMAN, Peter, 23 Dec. 1822, Nancy MOSER
BAKER, John, 30 Aug. 1828, Nancy LEATHERMAN.
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RootsWeb Family Trees: Peter LEATHERMAN (21 Jan. 1803 - 27 Sep. 1825) m. 23 Dec. 1822, Fredk. Co., MD, Nancy MOSER (3 July 1801 - 23 Aug. 1884, bu. Grossnickle's), d/o Jonathan MOSER & A. Maria LEATHERMAN.

I'm connected to Peter LEATHERMAN through my ancestors, who were his BOYER great-grandparents. (John) Adam BOYER (ca. 1701, Germany - Apr. 1755, York Co., PA) m. Anna Rosina, who moved to MD and remarried Michael B(E)IGLER. She left a will in Fredk. Co., MD. (Maria) Catharina BOYER, b. 22 Je. 1733, bpt. Christ Lutheran, York, PA, m. 1752, (John) Daniel LEDERMAN / LEATHERMAN (6 Nov. 1718, bpt. Langensoultzbach, Germany - by 11 Nov. 1797, will pr. 31 Jan. 1798, Fredk. Co., MD). Their son Peter LEATHERMAN (15 Nov. 1757 - 29 Nov. 1845, bu. Shady Grove, aka Sweigert-Ambrose-Leatherman Cem. near Ellerton) m. 25 Aug. 1786, (Anna) Mary SW[E]IGERT (9 Dec. 1764 - 10 May 1835) & had Peter, who m. Nancy MOSER. Daniel LEATHERMAN organized the German Baptist Church of Frederick, so you could check records of that church. I guess I should sort this out a bit.

Daniel LEATHERMAN was s/o (Johann) Theobald LEDERMAN & Anna Maria or Anna Margaretha ENGEL, who arrived 27 Sep. 1727, in Philadelphia on the James GOODWILL. Daniel m. Maria Catherina BOYER, b. 22 Je. 1733, and owned "Resurvey on Nazareth," & "German Plains" south of Wolfsville on Harp Hill Road. Children of Daniel & Catherina/Catherine:

Daniel LEATHERMAN (7 Oct. 175[3?] - 20 May 1799, bu. "Bucks Haunt" farm, Bethlehem, Wash., PA) m. ca. 1773, Elizabeth _
Rosina (ca. 175_ - 28 Dec. 178_)
Peter (15 Nov. 1757 - 29 Nov. 1845, MD) m. (Anna) Mary SW[E]IGER[T], qv
{Reverend} Michael (9 Jan. 1761, MD - 23 Sep. 1811, bu. near bro. Daniel, Bethlehem, PA) m. ca. 1783, Catherine PALMER [desc. to Licking Co., OH]
Susannah (1763 - 1804, Washington Co., PA) m. 1784, John MOSER (ca. 1765 - 1799) s/o Conrad
Catherine (5 Apr. 1765, MD - 22/23 Sep. 1844, New Philadelphia, Tuscarawas Co., OH) m. Nov. 1784, MD, as second wf/o Geo. CUSTER (3 Dec. 1744 - 13 Sep. 1829) [later attended Georges Creek Dunkard Church, Fayette Co., PA, & went to One Leg Twp., New Philadelphia, OH; desc. to Van Wert Co., OH].
Joseph (10 Dec. 1766 - 7 Dec. 1837, bu. Apples Lutheran Ref.) m1. Eliz. M. RECHER (27 Dec. 1758 - 1 Feb. 1818); m2, ca. 1820, Deborah _, bu. Pine Bank Cem., Gettysburg, PA.
Hannah, b. ca. 1770, MD, m. John BAKER
Anna Maria (ca. 1772, Ellerton, MD - 6 Oct. 1841, bu. Old Harmony Cem., Harmony, MD) m. 22 Apr. 1802, Isaac SCHRIVER, who d. 1827; also m. Jonathan MOSER (17[65?] - 24 Apr. 1836) s/o Conrad & Ann.
Magdalena (11 Aug. 1774 - by June 1843) m. Abraham MOSER & lived in Fayette Co., PA.
John (1776 - 21 Feb. 1867, bu. Brumbaugh Cem., near Gravelton, northern Kosciusko Co., IN) m. by Fredk. Co., MD, lic/o 20 Nov. 1798, Catherine MILLER (1777 - 16 Sep. 1850). They went to Tuscarawas Co., OH, then to Kosciusco Co., IN, where John preached & helped start the Turkey Creek German Baptist Church.
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Newspaper Abstracts: Rights of Man, Frederick, March 1794, Conrad MOSER, near Middletown, forewarns persons from purchasing bond given to Mr. HUNT.

Elizabethtown Advertiser, 15 Mar. 1798, the horse Paymaster to stand at John BAKER's, a mile from General SPRIGG's mill. (advertised by) James BREATHED.

Frederick, 13 Sep. 1797, meeting at home of John COOKERLY...Dr. John BAKER, Piney Creek...

Frederick, 27 May 1803, judges of election, Sixth District, Dr. John BAKER...

Letters at the Hagers Town P. O., 7 Jan. 1802, John BAKER, eight miles from Hagers Town.

Fredk. Herald, 28 Apr. 1810: Wood land for sale, 900 acres, adjoining plantations of the widow of Peter BUSSARD, Benj. HATHERLY, Peter LEATHERMAN, & John WISEMAN, on top of Kittoctin Mountain.
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Assessment Lists, 1798, Baltimore & Carroll Cos., Upper Gunpowder Hundred & Mine Run Hundred, John BAKER, 51 a. adjoining Margaret BAKER, who had 92 acres, adjoining Elizabeth ROSIER.
Taneytown & Piney Creek Hundred, District 6, John BAKER, part of Patients Care, 150 acres...
Frederick Co., Dist. 1., John BAKER, pt. Hammon Strife, 115 a.
Emanul {sic} BAKER, Resurvey on Walnut Bottom, Black Rock.
Henry BAKER, pt. Nicholas Chance, Trouble Enough, Bakers Delight.