Running Away With the Circus
In the 2013 Best American Essays edited by Cheryl Strayed, one of the essays ("Sometimes a Romantic Notion" from Gettysburg Review by Richard Schmitt), talks about running away with the circus and how no one ever calmly joins the circus, it's always a run. This got me thinking about titles whose main characters join the circus or which focus on circuses in some way.
The Final Confession of Mabel Stark by Robert Hough
"A novelization of the sensational life of the early twentieth-century female circus tiger trainer finds her reexamining her life, from her stint as a burlesque dancer after her escape from a mental institution to her five marriages and the devastating loss of her cats." Unrelated fun factoid: Actor Christopher Walken had a stint as a lion-tamer early on in his career.
Water for Elephants by Sara Gruen
Tipping the Velvet by Sarah Waters
Geek Love by Katherine Dunn
The Night Circus by Erin Morgenstern
The Circus, 1870s-1950s by Noel Daniel.
This book is massive, but highly rated. Includes little-known circus images by Stanley Kubrick and Charles and Ray Eames.
NYPL Digital Collections has numerous images of circuses from the Billy Rose Theatre Collection photograph file.