1.  J.H. Battle, W.H. Perrin, & G.C. Kniffin.  1887. Kentucky, a History of the State.  F.A. Battey & Co., Louisville, KY (excerpts online at the Kentucky Biographies Project [link died]):

EX-UNITED STATES SENATOR, WILLIS B. MACHEN was born April 5, 1810 in Caldwell, now Lyon County, Ky.  His parents, Henry and Nancy (Tarrant) Machen, came from South Carolina in 1809, located on a farm near where subject now resides.  The father was a prosperous farmer, and a man of much energy and good sense.  His death occurred in 1860; that of his wife in 1852.  There are only two of their children living - subject, and Frank, of Princeton, Ky.  The Machens are the out-growth of intermarriages on one side of Huguenots and Irish, and Scotch and English on the other.  Many of the ancestral connection, [sic] of Mr. Machen served the colonies with distinction during the war of Independence, among others was his great- grandfather Woods, who was killed by the Tories, and whose death was severely avenged by his brother, Col. Woods, of South Carolina.  Mr. Machen's early training was that common to farmer boys, attending the county schools in the winter and working on the farm in summer, but at the age of twenty entered Cumberland College, Princeton, Ky.  Leaving school, he engaged in the manufacture of iron with C.C. Cobb, in Livingston County, in which he was engaged for seven years, and in 1838 entered the mercantile business with no capital but a good name; meeting with reverses he failed three years after, but paid all debts, &c.  He then went to contracting and building turnpikes at which he was successful, but being severely hurt while thus engaged, he withdrew from hard labor, and in 1843, began the study of law; was admitted to the bar, and almost immediately built up a large clientage, practicing until 1850 in both Lyon and Caldwell Counties, when he retired to assume the management of a farm he had purchased where he now resides.  His fine brick residence is situated on a small hill, at the foot of which runs the Chesapeake & Ohio Railroad, and the Cumberland River, and on either side not over a mile distant are the towns of Eddyville and Kuttawa.  In 1849 Mr. Machen was a member of the convention that framed the present constitution of Kentucky, and in 1853 defeated his popular opponent, George W. Barbour, for the State senate.  He was elected to the lower house in 1855-60-61.  After the outbreak of the war he was elected by the convention while at Russellville, a member of the Provisional State Government, and served as chairman of that body for some months.  He was then elected a member of the Confederate congress by soldiers in the field and residents of his district, and served two terms; was reelected by the soldiers in the field alone the second time, and was a member of that body at the close of the war, when he made his escape to Canada.  He was soon after joined by his family, but was pardoned in three months by President Andrew Johnson, and returned home.  In 1872, upon the death of Garret Davis he was first appointed and then elected to fill his unexpired term in the United States senate.  In 1870, he was very strongly urged to accept the nomination for governor, but declined as there was a question as to his eligibility.  He has since refused to allow his name to be used before conventions for same office, although indorsed [sic] by many of the State papers.  In 1882, he was appointed by Gov. Blackburn one of the State railroad commissioners, which position he held two years.  Mr. Machen was first married to Margaret A. Lyon, youngest daughter of Chittenden and Nancy Lyon.  Two children of this union are still living.  His second wife was Eliza N. Dobbins of Eddyville.  His present wife, Victoria T. Mims, he married in 1859.  They are blessed with five children: Frank P., Willis B., Charles V., Minnie, now Mrs. A.D. Sayers, of Alabama, and Marjorie, his youngest child.

2.  Biographical Directory of the United States Congress (online at bioguide.congress.gov).