Interest Income. Interest income increased $70.1 million, or 31%, to $299.4 million for the nine months ended September 30, 2022, compared with $229.3 million for the nine months ended September 30, 2021. This increase was primarily attributable to an increase in higher average yields and loan balances.
The average balance of loans, including loans held for sale, during the nine months ended September 30, 2022 increased $661.7 million, or 8%, to $9.0 billion compared to $8.3 billion for the nine months ended September 30, 2021, and the average yield on loans increased 79 basis points, to 4.27% for the nine months ended September 30, 2022, compared to 3.48% for the nine months ended September 30, 2021.
The average balance of interest-earning deposits and other increased $15.7 million, or 2%, to $675.3 million for the nine months ended September 30, 2022, from the nine months ended September 30, 2021, and the average yield increased 32 basis points, to 0.63% for the nine months ended September 30, 2022, compared to 0.31% for the nine months ended September 30, 2021.
The average balance of securities held to maturity that were acquired in September 2022 was $33.1 million, while the average yield was 3.91% for the nine months ended September 30, 2022.
The average balance of mortgage loans in process of securitization decreased $190.8 million, or 42%, to $260.5 million for the nine months ended September 30, 2022, compared to the nine months ended September 30, 2021, while the average yield increased 42 basis points, to 3.01% for the nine months ended September 30, 2022, compared to 2.59% for the nine months ended September 30, 2021.
The average balance of taxable available for sale securities increased $35.5 million, or 12%, to $322.8 million for the nine months ended September 30, 2022, from $287.3 million for the nine months ended September 30, 2021, and the average yield decreased 20 basis points, to 0.87% for the nine months ended September 30, 2022, compared to 1.07% for the nine months ended September 30, 2021.
Interest Expense. Total interest expense increased $52.2 million, or 217%, to $76.3 million for the nine months ended September 30, 2022, compared with $24.1 million for the nine months ended September 30, 2021.
Interest expense on deposits increased $48.8 million, or 247%, to $68.6 million for the nine months ended September 30, 2022, from the nine months ended September 30, 2021. The increase was primarily due to increases in interest rates on interest-bearing checking and money market accounts, as well as higher average balances for certificates of deposit and money market accounts.
The average balance of interest-bearing checking accounts of $4.0 billion for the nine months ended September 30, 2022 decreased $653.0, or 14%, compared to $4.7 billion for the nine months ended September 30, 2021. The average yield of interest-bearing checking accounts was 1.03% for the nine months ended September 30, 2022, which was a 91 basis point increase compared to 0.12% for nine months ended September 30, 2021.
The average balance of money market accounts of $2.6 billion for the nine months ended September 30, 2022 increased $444.8, or 20%, compared to the nine months ended September 30, 2021. The average yield of money market accounts was 1.27% for the nine months ended September 30, 2022, which was a 51 basis point increase compared to 0.76% for nine months ended September 30, 2021.
The average balance of certificates of deposit of $1.3 billion for the nine months ended September 30, 2022 increased $746.3, or 147%, compared to the nine months ended September 30, 2021. The average yield of certificates of deposit was 1.31% for the nine months ended September 30, 2022, which was a 46 basis point increase compared to 0.85% for nine months ended September 30, 2021.
Interest expense on borrowings increased $3.3 million, or 79%, to $7.7 million for the nine months ended September 30, 2022 from the nine months ended September 30, 2021. The increase was due primarily to a 74 basis