I don't know what it is. It is not Coreopsis, which is quite hairy and has simple leaves, sometimes lobed at the base. This plant has compound leaves with 3 or perhaps 5 leaflets, and appears hairless and shiny.
Has classic Coreopsis lancelata foliage when photo is expanded. Hairiness is a feature of the species foliage, but subsp lanceolata can be close to glabrous. http://www.illinoiswildflowers.info/prairie/plantx/sand_coreopsisx.htm