Leslie's Ben Simpson (b: 16 Nov 1810??) was from Culpepper Co VA married to Mildred D Covington, (b: 17 Mar 1818 in Culpepper County,Virginia) Married: 3 Nov 1836 VA and spent time in Madison County KY before coming to Bates Co. Missouri between 1858 and 1861.
Buried in Dayton Cemetery. Killed June 1862 for failing to sell horses to Kansas Jayhawkers "unprovenced web family lore" Earned his living trading horses and farming.
His son Jeptha Reason Simpson (b 4 Jun 1858 Madison KY) continued to farm in Bates Co MO and died in 1924, His death certificate is here:
http://www.sos.mo.gov/TIF2PDFConsumer/DispPDF.aspx?fTiff=/archives/DeptofHealth/Death/1924/00037128.TIF&Fln=1389241.pdf

1860 Census listing for this Benjamin Simpson is as follows:

Name: Benj Simpson
Age in 1860: 50
Birth Year: abt 1810
Birthplace: Kentucky
Home in 1860: Deer Creek, Bates, Missouri
Post Office: Elk Fork
Household Members: Name Age
Benj Simpson 50
Milla Simpson 43
Polina Simpson 15
Mary E Simpson 13
Wm Simpson 11
Jas Simpson 9
Sophia Simpson 8
Milton Simpson 6
Jeptha Simpson 2

He and wife are found in the 1840 Madison Co KY census with 2 daughters, consistent with the above ages.
I can not tie him to the Cass County Home Guard or other civil war service.

There is also a Ben Simpson (b. 5 DEC 1810 Kentucky )found in Knox County as listed here in the 1887 county history. This Ben Simpson and family are often intermingled in web family trees with the one above but are NOT the same person. This Ben Simpson is buried in the family cemetery in Knox Co. MO. His Oath of Allegience is listed in the Provost Marshall papers for Knox C along with his son.

From the 1887 History of Lewis, Clark, Knox and Scotland Counties, Missouri:
E.A. and J.W. Simpson, twin brothers, were born March 2,1848, in Garrard County, Kentucky. Their parents, Benjamin and Paulina ( Arnold) Simpson were both natives of the same County and state. Mr. Simpson made farming his chief occupation while in Kentucky, and in 1857 immigrated to Knox County, Missouri, where he has resided ever since. To his first marriage eight children were born, all , save one, now living. They are Mollie Sever; Pauline Lindsey; Lucinda Young , who lives in Kansas; Malinda A. Belle ( deceased); Maggie E. Noel, of Lewis County, James M., of Novelty, and our two subjects, who reside in Missouri. After about 22 year of wedded life Mr. Simpson lost his wife, who was a Christian woman, and a daughter of Elijah Arnold. About 12 years later he married Miss Judith Lear, daughter of William Lear. To this marriage no children were born, and Mr. and Mrs. Simpson reside with our subjects, both of whom are enterprising and worthy young men, and inherit the hospitality and sociability usually attributed to native Kentuckians. December 30,1871, E. A. Simpson was united in marriage to Miss Mary E. Lear, daughter of W. Lear, and three of the four children born to this couple are now living as follows: Ada, Lottie and John W.. One child died in infancy. J.W. Simpson is a widower, having lost his wife over three years ago. This lady was Miss Mollie Smith, daughter of M.M. Smith. Our two subjects now jointly own a splendid farm of 140 acres, well stocked and improved and are regarded among the prominent farmers of the county. Their lives have been passed together, and they were educated at the same common schools. Both are Democrats and members of the Christian Church. E. A. is a member of the A.T.H.A. Professor James M. Simpson, a leading educator of Knox County, Missouri, his birth occurring January 1,1860. He is a son of Benjamin and Paulina ( Arnold) Simpson, the former a native of Kentucky, and born December 5,1819. He came to Missouri in the Spring of 1858, and settled on a farm in the Eastern part of Knox County, where he now lives. The mother was born in Kentucky in 1828, and died October 7,1864, in Knox County, Missouri. Our subject remained with his father until he reached his majority, before that time working hard and attending school whenever the opportunity offered. He borrowed money to pay for his first year in college, and then taught until he had accumulated enough money to enable him to complete his course in Missouri State Normal School, Kirskville, from which institution he graduate June 17,1886. He has taught about 8 years in all, and is now president of Oaklawn College, in Knox County, which position he has held for two years. July 1,1886, he was married to Miss Katie M. Funk, daughter of Thomas W. Funk, a native of West Virginia and Rachael ( Johnson) Funk, a native of Virginia.

The Ben Simpson of the 15th Kansas is listed in the 1915 Kansas census with his military service as follows:

Name: Ben Simpson Senior
Census Date: 1915
Residence County: Miami
Residence State: Kansas
Locality: Paola
Birth Location: Ohio
Family Number: 8
Gender: Male
Estimated Birth Year: abt 1836
Race: White
Line: 27
Roll: ks1915_148

He is neither of the above gentlemen.

So now I've stirred Bruce's muddy pot.
John R.