That's just about all I could find regarding him.
But if you Google on him and go into Images, you will find quite a number of examples of his work. It seems that Underwood was prolific and appeared in leading magazines of his day, including the Saturday Evening Post, the top general-interest magazine for more than half of the 20th century.
I have to admit that I don't care for most of Underwood's work. The scenes he depicts are usually bland (though that might have been because of the stories he illustrated). His compositions aren't usually very interesting, either. While he could draw well when he chose to, often enough his brushwork was just fussy enough to counteract the drawing. From Google, it seems that he used gouache, watercolor or possibly colored inks a good deal, this and the vignette style he often used suggest that he worked fairly fast. Given the quality of printing during his 1902 - early 1920s heyday, it's possible that the reproduction process smoothed over some of the rough brushwork.
For a quick look at some examples of his work in addition to what is displayed below, click here. The images shown below are what I consider among the best of his work.
Many Underwood illustrations deal with well-dressed couples. Apparently this is what the stories and art editors required.
I think this is one of his best efforts.
When given the chance or when in the right mood, Underwood could be witty.
A nondescript painting with large amounts of dead space surrounding the subjects. Was some of that covered with print in the publication?
By the woman's hair style, I'll assume this is one of Underwood's later works.