Doctors & Staff

Dr. Jeffery Korosec

Dr. Jeffery Korosec

Dr. Jeffrey Korosec graduated from the University of Wisconsin – Madison School of Veterinary Medicine in 1991. He joined the Elkhorn Veterinary Clinic in 1992, becoming a partner in 1999. Dr. Korosec is passionate about general veterinary practice, believing every pet should receive a thorough physical exam after which the owner should be given options that are in their pet’s best interest. Dr. Korosec’s special interests include soft tissue surgery, orthopedic surgery, and dentistry. His orthopedic surgical experience includes over 20 years of treating and managing injuries or surgical diseases related to all types of pets including racing greyhounds, agility, field trial, and hunting dogs. For over a year Dr. Korosec has had the unique opportunity of receiving one-on-one training with a board certified surgeon and is now proficient in a surgical procedure that changes the biomechanics of the canine knee (TPLO) for the treatment of cranial cruciate disease. During his time away from the clinic, Dr. Korosec volunteers at the Lakeland Animal Shelter and is on the advisory board for Gateway Technical College Veterinary Sciences Program. Dr. Korosec and his family live in the Elkhorn area with their menagerie of pets. He enjoys spending time with his family, hiking, swimming, and biking.


Nikki Preston

Nikki Preston

Dr. Nikki Preston grew up in the Chicago suburbs but spent her summers in Twin Lakes, WI where she currently resides. She completed her Bachelors of Science degree in Biology at Illinois Wesleyan University before graduating from the University of Illinois College of Veterinary Medicine in May 2015. Her special interests in veterinary medicine include internal medicine, dermatology, and imaging. Outside of work, she enjoys playing basketball, running, traveling, and spending time on the lake with her family and dog.


Dr. Colleen Stewart

Dr. Colleen Stewart

Dr. Colleen Stewart grew up in Williams Bay and currently lives in the area with her husband, three sons, adopted barn cats, a Green Wing Macaw, Yellow Crested Cockatoo, Red Lored Amazon, chinchillas, and an adopted Thoroughbred race horse off the track.  Dr. Stewart completed her undergraduate degree in Zoology at the University of California – Davis.  Then, she graduated from the University of Wisconsin Madison School of Veterinary Medicine in 1994.  She started working at the Elkhorn Veterinary Clinic in 1995.


Dr. Amanda Tucker

Dr. Amanda Tucker

Dr. Amanda Tucker After completing her undergraduate degree, Dr. Tucker went on to receive her masters degree in public health and in 2012 received her DVM from the University of Wisconsin. Her professional interests include internal medicine, public health, and small mammal exotics. In her spare time, Dr. Tucker enjoys hiking, swimming, biking, and running.


Dr. Ellen Waller

Dr. Ellen Waller

Dr. Ellen Waller received her Doctor of Veterinary Medicine from the University of Illinois in 1980. She worked in a mixed animal practice and then joined the Peace Corps, where she worked with a cattle cooperative in Africa. Dr. Waller has been engaged in small animal practice in this area since 1993, and joined Elkhorn Veterinary Clinic in December 2007. She enjoys all aspects of general practice and has special interests in feline medicine and surgery, geriatric care, dentistry, and animal behavior. Dr. Waller lives with her husband, Gianni, on a small farm in Woodstock, Illinois which they share with Lucky, the lab, and an assortment of cats, horses, goats, geese, and chickens.