I attach every useful Geraghty match from Belmullet. Maybe worth checking out the ones born before 1820 first off, especially those born in the 1700s. I'll leave it to you to have a look through these, they may help.
Michael Geraghty (same as the guy on Henry Bingham's marriage?) died in 1910, in the Workhouse, aged 92. Birth date c. 1818 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1910/05425/4516268.pdf.
Patrick Geraghty died in 1910, aged 82. Birth date c. 1828 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1910/05417/4513779.pdf. Informant was Michael Geraghty, his son.
Bridget Geraghty, "Spinster", died 1903, in Workhouse, aged 70. Birth date c. 1833 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1903/05651/4590695.pdf.
Pat Geraghty, died 1903, aged 74. Son John Geraghty informant. Birth date c. 1829 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1903/05659/4593183.pdfPatt Geraghty, died 1900, in Workhouse, aged 76. Birth date c. 1824 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1900/05767/4629624.pdfFrank Geraghty, died 1894, aged 70. Birth date c. 1824 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1894/05947/4689709.pdfMartin Geraghty, died 1893, aged 50. Birth date c. 1843 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1893/05999/4706751.pdfHugh Geraghty, died 1892, aged 63. Birth date c. 1829 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1892/06016/4712559.pdfHugh Geraghty, died 1892, aged 76, in Workhouse. Birth date c. 1816 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1892/06016/4712560.pdfMichael Geraghty, died 1892, aged 72, in Workhouse. Birth date c. 1820 - Same link as above.
John Geraghty, died 1891, aged 70. Birth date c. 1821 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1891/06060/4727547.pdfPatrick Geraghty, died 1887, aged 90. Birth date c. 1797 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1887/06220/4779760.pdfLarry Geraghty, died 1883, aged 85, in Workhouse. Birth date c. 1798 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1885/06294/4803750.pdfThomas Geraghty, died 1882, aged 44. This is a tragic case; he drowned "suffering from temporary insanity". Birth date c. 1838 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1882/06390/4834664.pdfJohn Geraghty, died 1883, aged 45, in Workhouse. Birth date c. 1838 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1882/06390/4834664.pdfOwen Geraghty, died 1881, aged 70, in Workhouse. Birth date c. 1811 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1881/06427/4846385.pdfMichael Geraghty, died 1868, aged 50. Birth date c. 1818 - Record is unavailable
Laurence Geraghty, died 1875, aged 76. Birth date c. 1799 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1875/020629/7237718.pdfStephen Geraghty, died 1875, aged 70. Birth date c. 1805 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1875/020610/7231489.pdfMichael Geraghty, died 1875, aged 95, in Workhouse. Birth date c. 1780 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1875/020629/7237720.pdfAnthony Geraghty, died 1869, aged 73. Birth date c. 1796 - Record unavailable.
Thomas Geraghty, died 1879, aged 84, in Workhouse. Birth date c. 1795 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1879/06523/4879273.pdfCharles Geraghty, died 1879, aged 57, in Workhouse. Birth date c. 1822 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1879/06513/4875567.pdfKitty Geraghty, died 1873, aged 35. Birth date c. 1838 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1873/020694/7260634.pdfAnthony Geraghty, died 1871, aged 60. Birth date c. 1811 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1871/020762/7283693.pdfMichael Geraghty, died 1871, aged 77. Birth date c. 1794 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1871/020780/7289416.pdfAnthony Geraghty, died 1871, aged 89. Birth date c. 1782 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1871/020753/7280777.pdfJames Geraghty, died 1871, aged 60. Birth date c. 1811 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1871/020762/7283694.pdfDaniel Gerrity, died 1870, aged 75. Birth date c. 1795 - No record available
James Gerraghty, died 1870, aged 40. Birth date c. 1830 - No record available
Stephen Geraghty, died 1872, aged 30. Birth date c. 1842 -
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1872/020714/7267854.pdfI haven't done the Castlebar matches yet! Cheers.