According to the Des Moines Register, “The city leased the land from Tallmadge E. Brown, a local lawyer and real-estate tycoon. Farmland and woods were transformed into the park during a four-month period” (Aug. 11, 1999). On the abstract for 632 40th Street, in April 1878, Tallmadge and Anna L. Brown: “Leases to grantee (Iowa State Agricultural Society) for a period of ten years, for the purpose of locating the State Agricultural Fair upon said grounds for the consideration of 10% of the total gate receipts.”
An excerpt was published in Bushnell’s 1881-82 Des Moines City Directory, which you can read at the State Historical Society of Iowa’s Library in Des Moines: “The grounds contain nearly one hundred acres, including a natural lake covering three and a half acres, which has an average depth of sixteen feet. The grounds are artistically laid out with carriage-ways and walks in good order, and have ornamental entrance and exit gates. The buildings are ample, tasteful and convenient; water is abundant, there being a system of water-works, with a powerful engine, and pipes laid throughout the grounds. The track is pronounced by horsemen as the best west of Chicago” (p. 84-85).