Coreopsis. Coreopsis spp..
Asteraceae, the daisy, sunflower or composite family.

Plant: Erect plant, 1'-2' high with showy, golden-yellow, daisy-like flowers on long stems. Perennial.
Flowers: Bright golden-yellow daisy-like heads, 1"-2" across with 20 or so toothed ray flowers, mostly solitary, on long stems.
Leaves: Opposite, compound, long-petioed, usually with five lanceolate leaflets, the terminal one being much larger than the side ones.
Fruit: A head with dark, winged achenes that sometimes stick to clothing or fur, hence the name "tickseed", given to some species
Blooming: June-August
Habitat: Open fields.

Comments: An unidentified species of coreopsis, this might be an escaped garden cultivar. The seeds stick to clothing and fur, and look a bit like ticks, giving rise to the common name Tickseed.

Where to find it: I have found this plant in one location in the upper meadow on the north side of the pond.