Between 1886 and 1889, Colonel Henry Exall, of Kentucky and Virginia, along with other investors, acquired the Cole property. The investors, from Philadelphia, Pennsylvania, formed the Philadelphia Place Land Association paying an average price of $377.00 per acre, totaling around $500,000.00.
Colonel Exall constructed a dam on Turtle Creek in 1890, creating Exall Lake, and began laying out the graveled streets. After a financial setback caused by the Panic of 1893, Colonel Exall farmed and raised trotting horses in this area he called lomo alto (Spanish for high land). In the 1890s, Exall Lake was a common picnic destination for Dallas residents.
In 1906, John S. Armstrong, the former partner of Thomas Marsalis, who developed Oak Cliff, sold his meatpacking business and invested his money in the former Philadelphia Place land, to develop it under the name of Highland Park. Armstrong, along with his two sons-in-law, Edgar L. Flippen and Hugh E. Prather, Sr., began making plans for developing the area. Armstrong chose the name for the town as it was located on high land that overlooked downtown Dallas. In 1907, Wilbur David Cook, the landscape designer who planned Beverly Hills, California, was hired to design its layout "as a refuge from an increasingly diverse city." Notably, twenty percent of the original land was set aside for parks. The first two lots were sold in 1909, in an area bounded by Armstrong, Abbott and Gillon Avenues and Hackberry Creek. A second development in Highland Park was developed in 1910.