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Abstract. Climate indices are important determinant of crop yields and therefore, quantifying long-term trend and their correlation with crop yield is critical for propositions ranging from food security to economic vivacity of agricultural management practices. Long-term trend of Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI), Palmer “Z” Index (ZNDX), growing degree days (GDD), and minimum temperature (T_min) during crop growing season (May-September) were analyzed for a period of 90 years (1927-2016) in 9 climate divisions of Illinois. Pearson correlation test at 95% confidence level was performed to determine the statistical correlation of detrended crop yield with these climate indices. The long-term trend analysis result for 1-month, 6-month, and 12-month SPI were found to have significant increasing trend in 8 out of 9, 6 out of 9, and 9 out of 9 climate divisions of Illinois at 95% confidence level. The PDSI did not show any significant trend in majority of the climate divisions whereas ZNDX was found to have significant trend in all climate divisions. The seasonal average increase in SPI01, SPI06, and SPI12 was found to be 0.003, 0.006, and 0.01 annually. The Pearson correlation test for correlation of corn and soybean yield with SPI01 and ZNDX was found significant whereas the yield was found poorly correlated with SPI06, SPI12, and PDSI in 6 out of 9 of climate divisions. GDD and T_min were also found to have significant trend in more than 7 out of 9 climate divisions. The minimum temperature exhibited positive trend with an average seasonal increment of 0.01 annually and GDD was found to have negative trend with an average seasonal declination of -0.90. Correlation test of corn yield with GDD was found significant in 8 climate divisions whereas soybean yield was found poorly correlated with both GDD and T_min.