This study aimed to identify the time to diagnosis among COVID-19 patients and factors associated with delayed diagnosis (DD). Data from COVID-19 patients in Gangwon, South Korea, diagnosed between 22 February 2020 and 29 January 2022, were analyzed, excluding asymptomatic cases and those who underwent mandatory testing. DD was defined as a period exceeding 2 or more days from symptom recognition to COVID-19 diagnosis. Univariate analysis was performed to investigate the demographic characteristics, COVID-19 symptoms, and underlying medical conditions associated with DD, followed by multivariate logistic regression analysis for significant variables. Among 2683 patients, 584 (21.8%) were diagnosed within a day of symptom onset. DD rates were lower in patients with febrile symptoms but higher among those with cough, myalgia, or anosmia/ageusia. High-risk underlying medical conditions were not significantly associated with DD. Older age groups, the Wonju medical service area, time of diagnosis between November 2020 and July 2021, symptom onset on nonworkdays, and individuals in nonwhite collar sectors were significantly associated with increased DD risks. These findings were consistent in the sensitivity analysis. This study underscores the need for enhanced promotion and system adjustments to ensure prompt testing upon symptom recognition.