Disclosed herein are methods for producing high density cellular arrays. In some embodiments, the methods comprise: providing a sample comprising a plurality of cells; and introducing the plurality of cells in the sample into microwells of a microwell array to produce a cellular array, wherein the microwell array comprises 500 or more microwells per inch2, and wherein 25% or more of the microwells of the cellular array comprise a single cell. The disclosed methods can be used for producing a high density synthetic particle array and a high density reagent array.