From Unknown Source:

The spring of 1865 saw the end of the war and the beginning of the Eureka Club's best season. Symbolic of the post-war expansion of baseball, the club opened their own new groiund. Located at the corner of Ferry and Adams streets in what is now called the "Ironbound" section of Newark, the new facilities were inaugurated in fine fashion on June 12 when the Eureka Club hosted the Athletics of Philadelphis.

From "Old South High Street":

Gen. Heber Breintnall (catcher) was one of the best of the old amateur Eureka Baseball Club players. The ball ground was a plot bounded by High, Mercer, West and Court Streets and Scribers Lane. From this gound the first professional baseball club was recruited, with the Wright Brothers as a nucleus.