A biography of William Keefer Martz Jr. is given in the History of Dauphin County by Luther Reily Kelker. It says he was the son of William Keefer Martz who was born on the farm of his father Jacob Martz near Sunbury. William Sr. started as a carpenter but later became a contractor who erected some of the most important buildings in Sunbury. He also did a lot of work for the PA Railroad Company and did the “big cut” at Herndon. He died at age 50 and had been a resident of Sunbury for 35 years.

He (William Sr.) married Elizabeth, daughter of Joseph and Elizabeth (Klein) Kline. This couple had children: William K Jr., Mary Ellen and Catherine S.

He is designated P6a2a.

The William Keefer Sr. in that article is clearly the William K Mertz listed by Floyd who he said married Susan Bowen and had daughter Margaret who married Frank Shipe. Meiser though says he married Elizabeth Bowen who was born in 1833. 

The key to sorting this out I think is Census analysis. It does seem clear William had children in 1850 but no wife, I assume she was deceased. One of those children was Anelia (Amelia?) age 4. I think she was the same girl now called Anelia C age 13 in 1860. The only other child in 1860 was Mary E age 1 -- a big gap. The wife in 1860 was indeed Elizabeth. And in 1880 (couldn't see them immediately in 1870), he's a carpenter like in 1850 and they have a 13 year old son William K.  

I believe this is the scenario that pertains. William married first Susan Bowen and she was the mother of those three young children living with William in 1850. Then he married Elizabeth Kline like the Dauphin County history says, probably in the late 1850’s. Meiser knew from Census his wife was named Elizabeth so he did what he typically did -- he just gave her the name Elizabeth Bowen to try to reconcile what he knew with what Floyd said.

A notice in a Sunbury paper dated 15 Mar 1856 seemed to indicate that William K Martz and John Bowen had been in some sort of partnership with J B Masser.

1850. His father had died, he lived with his mother and I would guess some of his own children (Margaret 7, Sarah 5 and Anelia 4) and some of his siblings (Mary 24 and Henry 13).

1860. William age 33 lived in Sunbury. Anelia C age 13 is a carryover from the 1850 household. And now there is a wife, Elizabeth, and a very young daughter Mary E age 1.

And he was still in Sunbury in 1870 and 1880.