Waldo Pentengill was born in Livermore Falls in 1844 and moved to Rumford in 1864 when his parents settled on a farm near Rumford Center. He became a farmer, school teacher, and a surveyor.

Pentengill went on to become prominent in Rumford civic life. He served as a selectman for 11 years and in 1890 was elected a State Senator.

He was the business agent for Hugh J. Chisholm when Chisholm was acquiring land for the power dam and paper mill.