Named after Jack Foster's wife Jennie and granddaughter Kathy, the Jennie K was built by the H. K. Porter Locomotive Company of Pittsburgh, Pennsylvania, in March 1940 (construction number 7084) as 0-4-0T engine #5 of the Acme Brick Company in Perla, Arkansas. #5 was sold in April 1957 to carousel band organ collector Paul Eakins of Sikeston, Missouri, who then sold the engine to the Stone Machinery Company in Daisy, Tennessee, in 1959 where it remained until 1963. Acquired by Cedar Point around 1964, Jennie K ran originally on the CP&LE as an 0-4-0 with tender and fake balloon stack. It is said to have arrived at the park "ready to run", so it may have served at another "Western" style park for a short time. It is also said that it had a four wheel tender when it arrived, but apparently the tender was soon traded for an eight wheel version. Sometime between the time Jennie K appeared in the 1966 Cedar Point brochure and 1971, Jennie's cowcatcher was moved forward and a pilot truck was added, making her a 2-4-0. She also had the fake balloon stack replaced with what appears to be the original shotgun stack making her perhaps the CP&LE's best proportioned engine.
By the late 1980s, Jennie K was out of service reportedly due to a need for firebox work. During the 2002 season, she was stored under a tarp behind the enginehouse. Jennie K's original Porter catalog specifications were as follows: 60" wheelbase, 31" drivewheels, 11" x 16" cylinders, overall length (original 0-4-0T) 18'-3", height 10'-0", weight in working order (as a saddletank engine) 42,000 lbs., original boiler pressure 170 PSI, tractive force 9020 lbs. (with saddletank), adhesion factor 4.66 (with saddletank), minimum rail weight recommended 40 lbs./yd.