Fluorescent conjugated polymers are attractive materials to produce low-cost and lightweight displays, lighting, and organic electronics. However, when transitioning from solution to solid state, maintaining the desired emissive properties of these materials remains a challenge; the emission wavelength and quantum yield of fluorescent polymers are highly sensitive to their solid state packing arrangements which are difficult to control or predict. Additionally, their susceptibility to photo-degradation limits their widespread use. Aggregation of the polymer can protect the material from most oxidative damage by reducing the diffusivity of the oxygen through the aggregate structure. Here we employ various bulk and single molecule fluorescence-based methods to explore this aspect of a well-studied organic semi-conductor, poly(3-hexylthiophene) (P3HT). Pre-aggregating P3HT with highly-polar solvents prior to spin casting leads to aggregate structures and thin films with significantly enhanced emissive intensity and photo-stability relative to films cast without pre-aggregation. Additionally, enhanced photo-oxidative stability was seen in films formed from the pre-aggregated samples. A better understanding of aggregate properties should lead to better control and higher performance of organic semiconductors in device applications.